NASA SP-2000-4519

Partners in Freedom

Contributions of the Langley Research Center to

U.S. Military Aircraft of the 1990’s

By

Joseph R. Chambers

Monographs in Aerospace History Number 19

The NASA History Series

National Aeronautics and Space Administration

Office of Policy and Plans

NASA History Division

Washington, DC

2000
Library of Congress Cataloging-in-Publication Data

Chambers, Joseph R.

Partners in freedom : contributions of the Langley Research Center to U.S. military

aircraft of the 1990’s / by Joseph R. Chambers.

p. cm. -- (NASA history series)

Includes bibliographical references and index.

1. Langley Research Center. 2. Aeronautics, Military--Research--United 

States--History. 3. Airplaces, Military--United States--Design and construction. I. Title.

II. Series.

UG644.H36 .C43 2000

623.7’46’072073--dc21

00-056072

The use of trademarks or names of manufacturers in this publication is for accurate

reporting and does not constitute an official endorsement, either expressed or implied, of

such products or manufacturers by the National Aeronautics and Space Administration.
Acknowledgments iii

Acknowledgments

I am sincerely indebted to the dozens of current and retired employees of the NASA

Langley Research Center who consented to be interviewed and submitted their personal

experiences, recollections, and files from which this documentation of Langley contributions was drawn. The following individuals contributed vital information to this

effort:

Special thanks to Bobby Berrier and Patricia A. West, who provided their superb technical editing and proofreading skills to the project. I would like to express my special gratitude to Noel A. Talcott and Jeffrey A. Yetter, who provided the inspiration to undertake

this activity, and to A. Gary Price, who provided the mechanism.

Thanks also to Percival J. Tesoro for the cover design, Leanna D. Bullock for assistance

with the photographs, Peggy S. Overbey for manuscript preparation services, Cathy W.

Everett for bibliography verification and formatting, Christine A. Ryan for printing

coordination, and Gail S. Langevin for editing and document production coordination.

Ultimately, however, the greatest thanks go to the thousands of current and retired

employees of the NASA Langley Research Center, who provided the personal dedication, expertise, and innovation that enabled the legendary contributions covered in this

work.

Joseph R. Chambers

Yorktown, VA

April 20, 2000

Irving Abel Stuart G. Flechner Linwood W. McKinney

William J. Alford, Jr. Charles H. Fox, Jr. James C. Newman, Jr.

Jerry M. Allen Charles M. Fremaux Luat T. Nguyen

Theodore G. Ayers William P. Gilbert James C. Patterson, Jr.

Donald D. Baals Sue B. Grafton John W. Paulson, Jr.

E. Ann Bare David E. Hahne Edward C. Polhamus

Bobby L. Berrier James B. Hallissy Richard J. Re

Ralph P. Bielat Perry W. Hanson Wilmer H. Reed, Jr.

James S. Bowman, Jr. Roy V. Harris, Jr. Rodney H. Ricketts

Francis J. Capone Lowell E. Hasel Charles L. Ruhlin

Huey D. Carden William P. Henderson Maynard C. Sandford

Stanley R. Cole Charles M. Jackson David S. Shaw

Mark A. Croom Lisa E. Jones M. Leroy Spearman

Richard G. Culpepper Joseph L. Johnson, Jr. Raymond D. Whipple

H. Benson Dexter Donald F. Keller Richard T. Whitcomb

Robert V. Doggett Richard E. Kuhn Thomas J. Yager

Robert H. Daugherty John E. Lamar E. Carson Yates

Moses G. Farmer Laurence K. Loftin, Jr. Long P. Yip

Donald L. Loving

Preface v

Preface

For over 80 years, Langley Research Center has exemplified the cutting edge of worldclass aeronautics research for civil and military aircraft. Established in 1917 as the

nation’s first civil aeronautics research laboratory under the charter of the National

Advisory Committee for Aeronautics (NACA), Langley initially existed as a small,

highly productive laboratory with emphasis on solving the problems of flight for the

military and the civil aviation industry. During World War II (WWII), the Langley

Memorial Aeronautical Laboratory directed virtually all of its workforce and facilities

to research for military aircraft. Following WWII, a more balanced program of military

and civil projects was undertaken. The emergence of the Space Age and the incorporation of the NACA and Langley into the new National Aeronautics and Space Administration (NASA) led to a rapid growth of space related research and the cultural change

of the old laboratory into a major research center. Today, Langley research efforts

encompass critical areas of both aeronautics and space technology.

Throughout its history, Langley has maintained a close working partnership with the

Department of Defense, U.S. industry, universities, and other government agencies to

support the defense of the nation with fundamental and applied research. Many of the

legendary contributions of Langley to military aircraft technology have been discussed

and documented by specialists, the media, and historians. Langley contributions to

famous military projects such as the aircraft drag cleanup studies of WWII, the advent

of supersonic flight and the X-1, the development and tests of the Century-series fighters, the X-15, and many, many others have been archived in detail.

The objective of this particular undertaking is to document the contributions of Langley

Research Center to specific military aircraft that were operational in the 1990’s. Virtually all military aircraft that participated in Operation Desert Storm, Kosovo, and other

peacekeeping missions of this era have Langley technical contributions to their design,

development, and support. In some instances Langley research from one aircraft development program helped to solve a problem in another development program. At the

conclusion of some development programs, Langley researchers obtained the research

models to conduct additional tests to learn more about previously unknown phenomena.

These data also proved useful in later developmental programs. Perhaps the most consistent element in all of the research programs is the length of time for the development

and maturation of new research concepts before they are implemented in new aircraft.

Many of the military aircraft in the U.S. inventory as of late 1999 were over 20 years

old. Langley activities that contributed to the development of some of these aircraft

began over 50 years prior.
vi Preface

This publication documents the role—from early concept stages to problem solving for

fleet aircraft—that Langley played in the military aircraft fleet of the United States for

the 1990’s. The declassification of documents and other material has provided an opportunity to record the contributions of Langley personnel and facilities and discuss the

impact of these contributions on Department of Defense aircraft programs. This review

is intended for the general public with an interest in aircraft development. For more

technical information about specific aircraft and programs, please see the publications

listed in the bibliography.

Readers familiar with NASA and its research centers will note that the former Lewis

Research Center is referred to by its new name, Glenn Research Center. The decision to

use the new name was made to avoid confusion for those readers less familiar with the

NASA centers and to avoid disruptive explanations in the text for all readers.
Contents vii

Contents

Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Langley Contributions to Selected Aircraft . . . . . . . . . . . . . . 3

BAI Exdrone BQM-147A. . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Highlights of Research by Langley for the Exdrone . . . . . . . . . . . . . . 5

Langley Contributions to the Exdrone BQM-147A . . . . . . . . . . . . . . . 7

Background. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Langley Research Efforts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Subsequent Exdrone Vehicle Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Boeing AV-8 Harrier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Highlights of Research by Langley for the AV-8 . . . . . . . . . . . . . . . . 11

Langley Contributions to the AV-8. . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Background. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Contributions to the P.1127 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Contributions to the Kestrel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Contributions to the AV-8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Boeing C-17 Globemaster III . . . . . . . . . . . . . . . . . . . . . . . . 21

Highlights of Research by Langley for the C-17 . . . . . . . . . . . . . . . . 21

Langley Contributions to the C-17. . . . . . . . . . . . . . . . . . . . . . . . . . . 23

The CX Competition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

The Externally Blown Flap Concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

The YC-15 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

The C-17 Supercritical Wing, Winglets, and Aerodynamic Studies . . . . . . . . . . . 26

Composite Materials. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Fly-by-Wire Control System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Avoiding the Deep Stall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Recognition Visit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
viii Contents

Boeing F/A-18 Hornet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Highlights of Research by Langley for the F/A-18 . . . . . . . . . . . . . . 29

Langley Contributions to the F/A-18 . . . . . . . . . . . . . . . . . . . . . . . . . 31

Vortex Lift and Maneuvering Flaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Development of the YF-17. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

F/A-18A to F/A-18D . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

Development of the F/A-18. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

Cruise Drag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

High-Angle-Of-Attack, Spin, and Spin Recovery Characteristics . . . . . . . . . . . . 36

The NASA High-Angle-Of-Attack Technology Program. . . . . . . . . . . . . . . . . . . . 38

The Falling-Leaf Maneuver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Flutter Clearance and Tail Buffet. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Thrust-Vectoring Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

F/A-18E/F. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

The Super Hornet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

Cruise Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Redesign of the Leading-Edge Extension . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

High-Angle-Of-Attack Characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

Spin Tunnel and Drop-Model Tests. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

Flutter Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Wing Drop. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Boeing T-45 Goshawk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

Highlights of Research by Langley for the T-45 . . . . . . . . . . . . . . . . 51

Langley Contributions to the T-45 . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

Early Configuration Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

Stall Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

Spin Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

Ground Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

Inlet Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

Fairchild Republic A-10 Thunderbolt II. . . . . . . . . . . . . . . . 57

Highlights of Research by Langley for the A-10 . . . . . . . . . . . . . . . . 57

Langley Contributions to the A-10. . . . . . . . . . . . . . . . . . . . . . . . . . . 59

The A-X Competition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

Spin Recovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

General Dynamics F-111 Aardvark . . . . . . . . . . . . . . . . . . . 61

Highlights of Research by Langley for the F-111 . . . . . . . . . . . . . . . 61

Langley Contributions to the F-111 . . . . . . . . . . . . . . . . . . . . . . . . . . 63

The Variable-Sweep Wing Concept. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

The Tactical Fighter Experimental (TFX) Program . . . . . . . . . . . . . . . . . . . . . . . 66

Aerodynamic Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68

Propulsion Integration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70

High-Angle-of-Attack Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

Spin Recovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
Contents ix

Flutter Tests. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .75

Crew Escape Module. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .76

Wing Box Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .78

The Transonic Aircraft Technology (TACT) Program . . . . . . . . . . . . . . . . . . . . . .78

The Mission Adaptive Wing (MAW) Program . . . . . . . . . . . . . . . . . . . . . . . . . . . .81

Grumman A-6 Intruder . . . . . . . . . . . . . . . . . . . . . . . . . . . . .83

Highlights of Research by Langley for the A-6 . . . . . . . . . . . . . . . . . 83

Langley Contributions to the A-6. . . . . . . . . . . . . . . . . . . . . . . . . . . . 85

Speed Brake Studies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .85

Spin Tunnel Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .85

The Composite Wing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .86

Grumman EA-6B Prowler . . . . . . . . . . . . . . . . . . . . . . . . . . .89

Highlights of Research by Langley for the EA-6B . . . . . . . . . . . . . . 89

Langley Contributions to the EA-6B . . . . . . . . . . . . . . . . . . . . . . . . . 91

Spin Tunnel Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .91

Maneuver Improvements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .91

Cooling Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .94

Grumman F-14 Tomcat . . . . . . . . . . . . . . . . . . . . . . . . . . . . .97

Highlights of Research by Langley for the F-14 . . . . . . . . . . . . . . . . 97

Langley Contributions to the F-14 . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

Early NASA Fighter Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .99

F-14 Source Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .100

NASA Independent Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .100

Propulsion Integration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .100

High-Angle-Of-Attack and Spin Research. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .102

Flutter Tests. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .106

F-14 Yaw Vanes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .107

Grumman X-29 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .109

Highlights of Research by Langley for the X-29 . . . . . . . . . . . . . . . 109

Langley Contributions to the X-29. . . . . . . . . . . . . . . . . . . . . . . . . . 111

Evolution of Forward-Swept Wing Configurations . . . . . . . . . . . . . . . . . . . . . . .111

High-Angle-of-Attack Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .112

Spin Tunnel Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .115

Drop-Model Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .117

Engine Inlet Tests. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .119

Aeroelastic Divergence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .119

Advanced Engine Nozzle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .120

Lockheed C-5 Galaxy . . . . . . . . . . . . . . . . . . . . . . . . . . . . .123

Highlights of Research by Langley for the C-5 . . . . . . . . . . . . . . . . 123

Langley Contributions to the C-5. . . . . . . . . . . . . . . . . . . . . . . . . . . 125

C-5 Evaluation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .125

Research on Sting Interference Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .125
x Contents

Research on Effects of Test Section Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125

Propulsion Integration Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127

Low-Speed and Wake Characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128

Tail Flutter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129

Load Alleviation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131

Ditching Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131

Wind-Tunnel Test to Flight-Test Correlation . . . . . . . . . . . . . . . . . . . . . . . . . . . 133

Lockheed Martin C-130 Hercules. . . . . . . . . . . . . . . . . . . . 135

Highlights of Research by Langley for the C-130 . . . . . . . . . . . . . . 135

Langley Contributions to the C-130. . . . . . . . . . . . . . . . . . . . . . . . . 137

Composite Structures and Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137

Advanced Cockpit Displays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137

Acoustics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137

Aerodynamic Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138

Recognition Visit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138

Lockheed Martin C-141 Starlifter. . . . . . . . . . . . . . . . . . . . 139

Highlights of Research by Langley for the C-141 . . . . . . . . . . . . . . 139

Langley Contributions to the C-141. . . . . . . . . . . . . . . . . . . . . . . . . 141

Tail Flutter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141

Aileron Reversal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143

Runway Grooving . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144

Wind Tunnel and Flight Correlation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144

Lockheed Martin F-16 Fighting Falcon . . . . . . . . . . . . . . . 147

Highlights of Research by Langley for the F-16 . . . . . . . . . . . . . . . 147

Langley Contributions to the F-16 . . . . . . . . . . . . . . . . . . . . . . . . . . 149

Early Assessments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149

Transonic Performance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149

Vortex Lift . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149

High-Angle-Of-Attack Stability and Control . . . . . . . . . . . . . . . . . . . . . . . . . . . 151

Curing Deep Stall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152

Spin Recovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153

Fly By Wire and Sidestick Controller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154

Flutter Clearance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155

The F-16XL. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156

Lockheed Martin F-22 Raptor . . . . . . . . . . . . . . . . . . . . . . 159

Highlights of Research by Langley for the F-22 . . . . . . . . . . . . . . . 159

Langley Contributions to the F-22 . . . . . . . . . . . . . . . . . . . . . . . . . . 161

The Advanced Tactical Fighter (ATF) Program . . . . . . . . . . . . . . . . . . . . . . . . . 161

Value of the Langley Database . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161

The YF-22 Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162

Letter of Appreciation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163

The F-22 Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163

Vertical-Tail Buffet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165
Contents xi

Lockheed P-3 Orion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .167

Highlights of Research by Langley for the P-3 . . . . . . . . . . . . . . . . 167

Langley Contributions to the P-3 . . . . . . . . . . . . . . . . . . . . . . . . . . . 169

The Lockheed Electra . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .169

Lockheed S-3 Viking. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .171

Highlights of Research by Langley for the S-3 . . . . . . . . . . . . . . . . 171

Langley Contributions to the S-3 . . . . . . . . . . . . . . . . . . . . . . . . . . . 173

Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .173

Spin Tunnel Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .173

Flutter Tests. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .174

McDonnell Douglas F-4 Phantom II . . . . . . . . . . . . . . . . . .175

Highlights of Research by Langley for the F-4 . . . . . . . . . . . . . . . . 175

Langley Contributions to the F-4 . . . . . . . . . . . . . . . . . . . . . . . . . . . 177

Early Configuration Development. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .177

Maneuverability. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .178

High-Angle-of-Attack Stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .179

The Flat Spin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .181

Nose Vibrations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .183

Runway Grooving . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .184

McDonnell Douglas F-15 Eagle . . . . . . . . . . . . . . . . . . . . .185

Highlights of Research by Langley for the F-15 . . . . . . . . . . . . . . . 185

Langley Contributions to the F-15 . . . . . . . . . . . . . . . . . . . . . . . . . . 187

The NASA Fighter Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .187

F-15 Source Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .188

Aerodynamic and Propulsion Integration Studies. . . . . . . . . . . . . . . . . . . . . . . .188

High-Angle-Of-Attack and Spin Research. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .190

Flutter Clearance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .191

The F-15 Short Takeoff and Landing and Maneuver Technology 

Demonstrator. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .192

Missiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .195

Highlights of Research by Langley for Missiles . . . . . . . . . . . . . . . 195

Langley Contributions to Missiles . . . . . . . . . . . . . . . . . . . . . . . . . . 197

Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .197

AIM-9 Sidewinder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .197

AIM-7 Sparrow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .199

AIM-120 AMRAAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .199

Impact on Aircraft Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .199

Northrop Grumman B-2 Spirit. . . . . . . . . . . . . . . . . . . . . . .201

Highlights of Research by Langley for the B-2 . . . . . . . . . . . . . . . . 201

Langley Contributions to the B-2. . . . . . . . . . . . . . . . . . . . . . . . . . . 203
xii Contents

Rockwell B-1B Lancer . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205

Highlights of Research by Langley for the B-1B. . . . . . . . . . . . . . . 205

Langley Contributions to the B-1B . . . . . . . . . . . . . . . . . . . . . . . . . 207

Early Strategic Bomber Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207

The B-1A Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208

High-Angle-of-Attack Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208

Cruise Drag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210

Flutter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211

The B-1B Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212

Dynamic Loads on Engine Nozzle Flaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212

Rockwell-MBB X-31 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213

Highlights of Research by Langley for the X-31 . . . . . . . . . . . . . . . 213

Langley Contributions to the X-31. . . . . . . . . . . . . . . . . . . . . . . . . . 215

Background. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215

The HiMAT Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215

The SNAKE Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216

X-31 Configuration Evolution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219

X-31 Flight Demonstration Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221

Role of the X-31 in High-Angle-of-Attack Technology . . . . . . . . . . . . . . . . . . . . 223

The Future—Investing in Freedom. . . . . . . . . . . . . . . . . . . 225

Wind Tunnels—The Tools of the Trade. . . . . . . . . . . . . . . 227

Langley 4- by 4-Foot Supersonic Pressure Tunnel. . . . . . . . . . . . . . 228

Langley 7- by 10-Foot High-Speed Tunnel . . . . . . . . . . . . . . . . . . . 228

Langley 8-Foot Transonic Pressure Tunnel . . . . . . . . . . . . . . . . . . . 228

Langley 30- by 60-Foot Tunnel . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229

Langley 16-Foot Transonic Tunnel . . . . . . . . . . . . . . . . . . . . . . . . . 229

Langley 20-Foot Vertical Spin Tunnel . . . . . . . . . . . . . . . . . . . . . . . 230

Langley 16-Foot Transonic Dynamics Tunnel . . . . . . . . . . . . . . . . . 231

Langley Unitary Plan Wind Tunnel . . . . . . . . . . . . . . . . . . . . . . . . . 232

Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243

Monographs in Aerospace History . . . . . . . . . . . . . . . . . . . 255

About the Author . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256
Introduction 1

Introduction

“The making available to agencies directly concerned with national defense 

of discoveries that have military value or significance....”

The foregoing statement is an excerpt from the National Aeronautics and Space Act of

1958, which in part established the formal relationship between NASA and those

responsible for the defense of the nation. Since its initial operations over 80 years ago,

the Langley Research Center has maintained an appropriate priority within its research

activities to ensure the quality, timeliness, and applications of its research in accordance

with this congressional act. As a result, Langley and the Department of Defense (DOD)

have maintained a strong and productive relationship. This critical teamwork has been

nurtured by mutual respect and recognition that the close working arrangements have

benefited both parties. 

Langley’s support of specific military aircraft development programs and Langley’s fundamental research have provided many benefits to the DOD. By virtue of its independent agency perspective, Langley’s assessments of evolving technology and aircraft

systems have provided, and continue to provide, the DOD with unbiased analysis, opinions, data, and extremely valuable recommendations for decisions about aeronautical

technology issues in its aircraft programs. Langley’s staff has been frequently called

upon to participate or represent the DOD in early assessments and selections of competing aircraft designs. In addition, Langley’s unique wind tunnels, simulators, and computational facilities have been extensively utilized for evaluations and development of

military aircraft. The DOD benefits from the extensive experiences and corporate

knowledge of the Langley staff as a result of Langley’s participation in a vast number of

aircraft development programs. The multidiscipline expertise at Langley is viewed as a

unique capability and resource for the nation. 

The DOD frequently requests the participation of Langley on review boards and accident investigations. The DOD also recognizes that technical problem-solving exercises

during aircraft development programs frequently do not provide the fundamental understanding or design tools necessary to avoid similar problems in future aircraft programs.

Therefore, the DOD encourages Langley to conduct follow-on research and frequently

assists NASA in obtaining the resources required for these efforts.

Finally, the DOD and its supporting industries value the innovative concepts and technical capabilities provided by the ongoing fundamental research programs at Langley.

Breakthrough concepts in aeronautics take years of dedicated research to bring to maturity and readiness for application. Many examples are discussed herein where Langley

conceived, assessed, and reduced the risk of application of enabling technology when
2 Introduction

that technology was critically needed for the development of major DOD aircraft

programs.

Providing support to the DOD in the development of military aircraft has provided

Langley with very significant benefits. By responding to DOD’s requests, Langley

maintains relevance in research endeavors and receives test assets, valuable data, and

validation of research concepts. For example, DOD normally provides wind-tunnel

models for assessments in Langley’s unique wind-tunnel facilities. (For more information about selected Langley wind tunnels, see the appendix.) After the critical objectives

of aircraft development programs have been met, these models are frequently made

available to Langley researchers for generic research and assessments of advanced concepts, which provides a mechanism for research studies that might not be otherwise

funded within the Langley budget.

By participating in problem-solving exercises with DOD, Langley researchers are

exposed to a myriad of real-world requirements and constraints, thereby gaining valuable awareness of limitations in designing and conducting research within specific technical disciplines. Researchers also experience the implication of off-design flight

conditions on new technologies, and thus obtain a much broader outlook for future

research opportunities. Another valuable benefit to Langley is the application and validation of research concepts and technical analysis methods. By becoming a team member in DOD aircraft development programs, Langley researchers obtain highly valued

flight-test data and feedback that is unaffordable within NASA budget constraints. 

The single most important benefit of the DOD and Langley partnership, however, is the

application of new technologies to this nation’s first-line military aircraft, thereby helping to ensure the continued supremacy of the airpower of the United States.
Langley Contributions to Selected Aircraft 3

Langley Contributions to Selected 

Aircraft

The recent declassification of many documents detailing research conducted at Langley

during the 1960’s, 1970’s, 1980’s, and 1990’s has permitted a unique opportunity to collate and summarize the contributions of Langley researchers to several types of aircraft. 

The following pages document specific contributions of the NASA Langley Research

Center to U.S. military aircraft. The discussion includes fighters, transports, trainers,

missiles, and remotely piloted vehicles. The information, which has been gathered from

documents, personal interviews, and other sources, emphasizes the highlights of Langley’s support of specific programs. Research on developing aircraft is extensive and

exhaustive. In many cases, additional projects or research was conducted on specific aircraft; however, not all activities are covered herein.

The Langley research culture that produced these significant results flourished because

of team participation and the personal dedication and contributions of many, many

individuals. Despite the dangers of citing certain individuals and omitting others,

names have been included for further guidance to those interested in expanding the

information.

The material is presented in two formats. These formats are

• Single-page (back and front) overviews that summarize the major contributions of 

Langley to a specific aircraft 

• Multipage detailed discussions of individual contributions to a specific aircraft 

The discussion is intentionally at a level that can be understood by the nontechnical

reader; however, additional publications are provided in the bibliography for those seeking more detailed technical information.

Highlights of Research by Langley for the Exdrone

BAI Exdrone BQM-147A 5

BAI Exdrone BQM-147A

HIGHLIGHTS OF RESEARCH BY LANGLEY FOR THE EXDRONE

1. At the request of the U.S. Marine Corps, Langley conducted wind-tunnel and flight

tests to solve unacceptable Exdrone low-speed flight characteristics. 

2. Langley identified configuration modifications to the wing airfoil, control surfaces,

wing leading edge, and vertical tail that dramatically improved low-speed flight

characteristics.

SPECIFICATIONS

Manufacturer

BAI Aerosystems, Inc.

Date in service

Late 1980’s

Number built

Over 500 to date

Type

Remotely piloted vehicle

Crew

Remotely piloted

Engine

8-hp 2-stroke gasoline 

engine, 2-blade wooden 

propeller

MISSION

Reconnaissance, communications jamming, and delivery of 

nonlethal payloads

USERS

U.S. Marine Corps and U.S. 

Naval Air Warfare Center

DIMENSIONS

Wingspan. . . . . . . . . . . . . 8.2 ft

Length . . . . . . . . . . . . . . . 6.1 ft

Height . . . . . . . . . . . . . . . 1.7 ft

Wing area. . . . . . . . . . 21.4 sq ft

WEIGHT

Empty . . . . . . . . . . . . . . . 45 lb

Max payload . . . . . . . . . . 46 lb

PERFORMANCE

Cruise speed . . . . . . . . 90 mph

Range. . . . . . . . . . . . . . . . 50 mi

Endurance . . . . . . . . . . . . . 2 hr
Highlights of Research by Langley for the Exdrone

6 BAI Exdrone BQM-147A

The worldwide deployment of remotely piloted vehicles (RPV’s) by military forces has

dramatically increased. Several factors, such as elimination of threats to human pilots in

hostile environments, cost-effectiveness for certain missions, and stealth for some applications, have stimulated the use of RPV’s. The field-launched Exdrone RPV has proven

to be an extremely effective battlefield option for the U.S. Marine Corps. During Operation Desert Storm, Exdrone was pulled from a research and development program. The

Exdrone was pressed into reconnaissance service to find attack routes through Iraqi

defenses, thus allowing a rapid ground advance into Kuwait. The NASA Langley

Research Center made a critical and timely contribution during the development of the

Exdrone that enabled highly successful deployments of the vehicle.

In the mid-1980’s, prior to the involvement of Langley, BAI Aerosystems, Inc. manufactured the Exdrone RPV in accordance with a technical specification generated by Johns

Hopkins University Applied Physics Laboratory. This version of the Exdrone was for an

earlier mission (jamming of communications) that required high dash speeds, therefore,

the configuration was not optimized for the low-speed flights that are necessary for

extended reconnaissance missions. In fact, at slow speeds the vehicle was extremely difficult to fly and several crashes occurred during field trials simulating the reconnaissance task.

In response to an urgent request from the Marine Corps in 1988, Langley conducted

wind-tunnel and flight tests of the Exdrone to determine how the vehicle could be modified to enhance the flight characteristics in low-speed flight. Changes to the wing airfoil,

control surfaces, wing leading edge, and vertical tail that were recommended by the

Langley staff resulted in a configuration with outstanding low-speed flight characteristics. The changes were incorporated into the BQM-147A Exdrone. The modified vehicle

was an immediate success in reconnaissance missions in Operation Desert Storm.

The overall aerodynamic configuration of the Exdrone has not been revised since

Langley’s study; however, the vehicle payloads and mission applications continue to be

upgraded. The latest vehicle is referred to as the Dragon Drone. As technological innovations continue to evolve candidate payloads into smaller, more efficient packages that

are suitable for small RPV’s, the Dragon Drone’s capabilities will likewise continue to

be upgraded. The nucleus of the concept, however, remains the modified configuration

that owes much to the improvements recommended by Langley’s insightful researchers

and their problem-solving efforts.
Langley Contributions to the Exdrone BQM-147A

BAI Exdrone BQM-147A 7

LANGLEY CONTRIBUTIONS TO THE EXDRONE BQM-147A

Background BAI Aerosystems, Inc. (BAI) of Easton, Maryland initially manufactured the Exdrone

air vehicle in the late 1980’s in accordance with a technical specification generated by

the Johns Hopkins University Applied Physics Laboratory (JHU-APL). JHU-APL’s

delta-wing configuration was powered by a tractor propeller propulsion system. This

configuration was effective for an earlier mission for jamming of communications that

required high dash speeds, therefore the configuration was not optimized for the lowspeed flights that are necessary for extended reconnaissance missions. During evaluation for potential reconnaissance applications, the U.S. Marine Corps found that the

vehicle exhibited poor stability and control characteristics and had a tendency toward

severe lateral-directional instability near the stall, which resulted in numerous crashes.

At the request of the Marine Corps in 1988, exploratory wind-tunnel and flight-test

investigations of the Exdrone were conducted at the Langley Research Center by flight

dynamics specialists under the lead of Joseph L. Johnson, Jr. Lead researcher for the

study was Long P. Yip.

Langley Research Efforts Results of wind-tunnel tests of the baseline Exdrone configuration in the Langley

12-Foot Low-Speed Tunnel identified several aerodynamic deficiencies that contributed

to the unacceptable low-speed flight characteristics experienced in the Marine Corps

evaluations. For example, longitudinal control was insufficient to trim the Exdrone to

the high-lift conditions required for low-speed flight. Yip recommended an increase in

the chord of the elevator and thereby provided almost three times as much lift for lowspeed flight. To cure a wing-dropping tendency at high lift, Yip recommended a leadingedge “droop” modification to the outer wing panels. Increasing the rudder area and the

size of the vertical tail solved deficiencies in directional stability and control. The original configuration displayed a bad combination of lightly damped rolling and yawing

motions (sometimes called Dutch roll), but Yip eliminated this motion by increasing

directional stability with the increased vertical tail and by adding wingtip skids. The

wingtip skids also provided better flow over the ailerons and served as landing skids,

which replaced the original drag-producing wire skids.

Langley researchers Long P. Yip and David Fratello

with modified Exdrone during flight-test evaluation.
Langley Contributions to the Exdrone BQM-147A

8 BAI Exdrone BQM-147A

One noteworthy modification contributed by NASA was a sawtooth notch on the wing

leading edge near the wingtip. This notch and the leading-edge droop mentioned earlier

were an outgrowth of the Langley General Aviation Stall-Spin Program. Yip and his

peers had previously recommended the combination to certain general aviation companies for increasing stall departure and spin resistance with a minimal drag penalty. Thus,

NASA research to improve light aircraft provided a critical improvement for military

applications. As a result of these improvements, the Exdrone is easily flown by inexperienced pilots and very forgiving during training maneuvers.

The results of radio-controlled flight tests conducted by Langley researchers at the

Langley Plum Tree Test Site, located in nearby Poquoson, VA, showed that the modified

configuration had excellent longitudinal and lateral-directional flight characteristics.

The configuration was very maneuverable and responsive to control inputs, exhibited

good damping characteristics, and was easily flyable through the stall with no departure

tendencies.

The modifications recommended by Langley were endorsed and applied to the Exdrone

design, and the overall aerodynamic configuration of the Exdrone vehicle has not

changed since these modifications.

Subsequent Exdrone Vehicle 

Applications

In early 1990, approximately 30 of the newly configured BQM-147A Exdrone reconnaissance RPV’s were sent to Operation Desert Storm. The Exdrones were successfully

used to map Iraqi minefields and bunkers, which allowed the Allied ground forces to

slip through in darkness. During the 1990’s, several hundred Exdrone air vehicles were

produced by BAI under contract to the U.S. Uninhabited Air Vehicle Joint Project Office

(UAV-JPO). These vehicles were sent to Army and Marine Corps units as cost-effective

devices for familiarizing new users with the benefits of tactical unmanned reconnaissance systems. 

Throughout the 1990’s, the UAV-JPO directed BAI, the Department of the Navy, and the

Army Research Laboratory to test and incorporate numerous payloads and system

upgrades for the basic Exdrone aircraft. Some of those upgrades include Global Positioning System (GPS) (Exdrone was among the first military aircraft certified to use

GPS for navigation), a communications relay, the Tactical Remote Sensor Suite (TRSS),

an infrared and several other versions of down-looking reconnaissance sensors, and a

parachute recovery system to protect the higher value payloads.

In early 1997, the Marine Corps provided funds to BAI to create a new configuration of

the Exdrone (referred to as Dragon Drone) for the Hunter-Warrior Advanced Warfighting Experiment at Twenty-Nine Palms, CA. Tests performed at NASA Wallops Flight

Facility successfully identified and led to the elimination of onboard vibration interference with reconnaissance payloads. A belly-mounted pan-tilt-zoom television camera

produced by BAI was then installed into Dragon Drone with several other improvements.

During the Hunter-Warrior Experiment, Dragon Drones proved highly effective in identifying enemy command locations and troop movements at distances of up to 30 mi.

Because of the success of the Hunter-Warrior Experiment, the Marine Corps funded the

development of other upgrades to the Dragon Drone system, including

• Belly-mounted television camera equipped with laser range finder for enhanced 

targeting 
Langley Contributions to the Exdrone BQM-147A

BAI Exdrone BQM-147A 9

• Belly-mount infrared camera equipped with laser range finder for enhanced targeting 

at night

• Pneumatic launcher and deck-mounted net recovery system to enable shipboard use

• Belly-mounted dispenser for insertion of nonlethal warfare agents (i.e., tear gas)

The Marine Corps’ success with the Dragon Drone has sparked worldwide interest in

the system. BAI Aerosystems, Inc. received the first international order for a Dragon

Drone system from the Bahrain Defense Force (BDF) with delivery in late July 1999. A

small Dragon Drone system is being leased to the Australian Marines for evaluation.

The Ministry of Defense of the United Kingdom is investigating the feasibility of

Dragon Drone providing turnkey fulfillment of their tactical UAV requirements. Several

U.S. organizations, including the Air Force and Coast Guard, are actively pursuing these

systems. 

Clearly, the future for the Dragon Drone is bright. As technological innovations continue to evolve candidate payloads into smaller, more efficient packages that are suitable

for RPV’s, the Dragon Drone’s capabilities will likewise continue to be upgraded. The

nucleus of the configuration, however, remains the vehicle configuration that came from

the timely and responsive improvements recommended by insightful researchers at

Langley.

An Exdrone undergoes weight and balance tests.

Highlights of Research by Langley for the AV-8

Boeing AV-8 Harrier 11

Boeing AV-8 Harrier

HIGHLIGHTS OF RESEARCH BY LANGLEY FOR THE AV-8

1. Free-flight model tests and powered-model studies of the P.1127 by Langley instilled

confidence in Hawker’s commitment and converted many skeptics in the United

Kingdom.

2. Flight tests and coordination by the Langley chief test pilot provided guidance to the

British and kept the U.S. and NASA in partnership with leading-edge vertical and

short takeoff and landing (V/STOL) developments.

3. Langley flight research and engineering development of vectoring in forward flight

(VIFF) provided the Harrier with unprecedented maneuver options in air-to-air

combat.

4. Langley provided independent tests and analysis of a deficient competing V/STOL

fighter concept (XFV-12A).

5. Langley provided wind-tunnel database for design of AV-8B wing, including beneficial flap and power effects and supercritical airfoil which provide tremendous

increase in STOL load carrying capability over previous versions of the AV-8.

SPECIFICATIONS

Manufacturer

Boeing

Subcontractor

British Aerospace

Date in service

November 1983

Type

V/STOL close support

Crew

One

Engine

Rolls Royce F402-RR-408

USERS

U.S. Marine Corps, British 

Navy, British Air Force, Spanish 

Navy, and Italian Navy

DIMENSIONS

Wingspan. . . . . . . . . . . . 30.3 ft

Length . . . . . . . . . . . . . 47.75 ft

Height . . . . . . . . . . . . . . 11.6 ft

Wing area. . . . . . . . . 230.0 sq ft

WEIGHT

Empty . . . . . . . . . . . . 14,867 lb

Max VTOL . . . . . . . . 20,595 lb

PERFORMANCE

Max speed . . . . . Mach number

of 1.0
Highlights of Research by Langley for the AV-8

12 Boeing AV-8 Harrier

The Langley Research Center has played a key role for over 40 years in the highly successful development of the Boeing (formerly McDonnell Douglas) AV-8 Harrier—the

most advanced vertical and short takeoff and landing (V/STOL) high-performance aircraft in the world. Langley has been involved in the development of the Harrier since the

conceptual and evolutionary stages and continuing through the P.1127 prototype, the

Kestrel (XV-6A), the AV-8A, and the current AV-8B used by the U.S. Marine Corps.

Langley’s initial involvement with the Harrier began when the British Hawker Company

designed a V/STOL prototype known as the P.1127 in 1957. Unfortunately, Hawker’s

revolutionary design was met with disinterest by the British government and a lack of

government funding to proceed into development. At that time, experts at Langley had

conducted extensive research on numerous competitive concepts for V/STOL flight,

including aircraft-tilting (tail sitters), thrust-tilting (tilt rotors), thrust-deflection

(deflected slipstream), and dual-propulsion (lift-cruise engines) concepts. The simplicity and elegance of the rotatable nozzle vectored-thrust concept of the P.1127 so

impressed Langley management and researchers that a formal agreement for cooperative testing was initiated with Hawker under the Mutual Weapons Development Program of NATO. Free-flying tests of a 1/6-scale model were conducted in the Langley

30- by 60-Foot (Full-Scale) Tunnel to evaluate flying characteristics and to demonstrate

the ease of converting between hovering flight and conventional wing-borne forward

flight. These dramatic model flight tests provided confidence to the Hawker test pilots

and design team and helped sway the opinions of skeptics in the United Kingdom. Transonic wind-tunnel tests of a powered P.1127 model were also conducted in the Langley

16-Foot Transonic Tunnel. In recognition of his preeminent position as the world leader

in flight testing of V/STOL aircraft, Langley chief test pilot John P. (Jack) Reeder was

invited to evaluate the P.1127 aircraft and became a strong supporter of the concept.

Following cooperative flight-test evaluations of the second-generation P.1127, the

Kestrel, by military of the United Kingdom, the United States, and the Federal Republic

of (West) Germany, Langley was provided with two aircraft. These aircraft were used to

conduct extensive flight tests to develop more time- and fuel-efficient instrument

approach procedures. Arguably, Langley’s most significant contribution to the Kestrel

was the flight research and engineering development of the vectoring in forward flight

(VIFF) concept for enhanced maneuverability in air-to-air combat. This capability provides the Harrier pilot with unique maneuver options. Other Langley contributions

included wind-tunnel databases to optimize wing-flap-nozzle aerodynamic interactions

and the supercritical wing design methodology for the AV-8B. Langley’s leadership role

in V/STOL technology was transferred to the NASA Ames Research Center in 1973

where NASA support for the AV-8 series continues. Langley supports the program in

technical disciplines that are unique to Langley, such as spin tunnel tests of new

variants.
Langley Contributions to the AV-8

Boeing AV-8 Harrier 13

LANGLEY CONTRIBUTIONS TO THE AV-8

Background In the early 1950’s, the Langley Research Center was recognized worldwide as a leader

in fundamental and applied research on vertical takeoff and landing aircraft. Leaders in

the Langley research efforts included John P. Campbell, Richard E. Kuhn, John P. (Jack)

Reeder, and Marion O. McKinney. The challenge of providing efficient vertical flight

with minimal penalties and adequate payload produced a myriad of candidate concepts,

including aircraft-tilting (tail sitters), thrust-tilting (tilt rotors), thrust-deflection

(deflected slipstream), and dual-propulsion (lift-cruise engines) concepts. The Langley

researchers had accumulated in-depth experience with each concept and had identified

the limitations and complexities that constrained the satisfactory growth of vertical and

short takeoff and landing (V/STOL) aircraft. In view of this vast experience and their

innovativeness and visionary personalities, the researchers were actively sought for

assessments and opinions of emerging V/STOL concepts.

In the United Kingdom, Hawker Aircraft Ltd. was privately funding the development of

a new V/STOL tactical strike aircraft known as the P.1127. Initial interest from the British government had been lukewarm, and Hawker aggressively pursued potential funding

from the Mutual Weapons Development Program (MWDP) of the North Atlantic Treaty

Organization (NATO) for development of the revolutionary P.1127 engine. This engine

utilized four swiveling nozzles to redirect the engine thrust for vertical or forward flight.

The U.S. members of the MWDP were particularly impressed with the P.1127 concept,

and with their outspoken leadership, critical development funds were provided to Bristol

Siddeley, the engine manufacturer, in June 1958.

The support for the P.1127 project from the U.S. military (particularly the Marine

Corps) and NASA has been a key element in the success of the Harrier, which continues

to the present day.

Contributions to the P.1127 As Hawker proceeded in the engineering development of the P.1127 from 1959 to 1960,

numerous critical issues arose. These critical issues included the design of the flight

control system; whether artificial stabilization was required; the lifting capability of the

aircraft in ground effect; and the stability, control, and performance of the P.1127 in

conventional flight. Perhaps the most daunting question was whether the aircraft could

satisfactorily perform the transition from hovering flight (supported by the vertically

directed engine thrust) to conventional wing-borne flight. Many skeptics—particularly

in the British government—believed that the transition maneuver would be far too complex for the pilot or that the P.1127 would not maintain adequate lift to permit a safe

conversion.

John Stack, then Assistant Director of Langley and an active member of the MWDP,

regarded the P.1127 as the most significant advance since the achievement of operational supersonic speeds in fighters. Stack directed the Langley team to provide full support to the emerging P.1127 technology by conducting tests in the unique facilities at

Langley. Two model test programs were initiated. One, free-flight tests of a 1/6-scale

dynamically scaled powered model in the Langley 30- by 60-Foot (Full-Scale) Tunnel,

was used to determine the characteristics of the P.1127 in the transition maneuver. The

other program used a large-scale powered model (with simultaneous simulation of inlet

and exhaust flows) for force tests in the Langley 16-Foot Transonic Tunnel to determine

the complex propulsion and airframe interactions over the operational flight envelope.

The 1/6-scale model was also used for tests on the Langley Control Line Facility (a
Langley Contributions to the AV-8

14 Boeing AV-8 Harrier

large rotating crane equipped with control lines for testing powered models) to determine characteristics during rapid transitions to and from hovering flight. All tests were

slated for completion prior to the initial flights of the prototype aircraft in 1961.

Under the direction of Marion McKinney, the free-flight model tests showed that the

P.1127 model behaved extremely well when compared with other V/STOL designs

tested by Langley. Transitions to and from forward flight were easily performed, and

thrust management was relatively simple. Several problems were identified, however,

including the fact that the model lacked sufficient lateral control power for satisfactory

behavior during the transition. (The control power of the aircraft was increased as a

result of these tests.) A tendency to pitch up due to longitudinal instability at high angles

of attack was anticipated based on Hawker wind-tunnel tests and was readily apparent in

the model flight tests. (This problem was subsequently cured by adding anhedral or

droop to the horizontal-tail surfaces of the P.1127 and subsequent variants.) Despite

these shortcomings, the P.1127 was judged to be a superior performer by the Langley

researchers.

The free-flight model tests were witnessed by leaders of the Hawker design team,

including William Bedford, the P.1127 test pilot slated to make the first conversion

flights of the aircraft. While at Langley, Bedford flew Langley’s variable stability

research helicopter, which had been programmed to simulate the control powers and

sensitivities of the P.1127 design. The variable stability features of the helicopter provided valuable information that was used by Hawker in the control system design of the

P.1127.

Shielded by a protective panel, Langley researchers

Robert O. Schade and Louis P. Tosti hover the 1/6-scale free-flight

model in the airflow return passage of the Full-Scale Tunnel.
Langley Contributions to the AV-8

Boeing AV-8 Harrier 15

Hovering flight tests of the P.1127 were conducted in the United Kingdom on

October 21, 1960, followed by the first conventional flight on March 13, 1961. Finally,

on September 12, 1961, transition flights both to and from wing-borne to jet-borne flight

were accomplished. The overall results of these flight programs agreed remarkably well

with the Langley model tests and the helicopter in-flight simulations of 1960. John

Stack witnessed transition flights in gusty conditions a week later and referred to them

as the smoothest transition of any of the existing crop of V/STOL machines. Stack subsequently noted that the precursor Langley tests had, in fact, indicated that the P.1127

would have better characteristics than any other concept previously investigated.

Perhaps the most important compliment to the Langley contributions prior to the first

flights came from Sir Sydney Camm, the Chief Designer of Hawker (designer of the

Hawker Hurricane fighter of WW II), who said that the Langley wind-tunnel tests were

the most important tests for the P.1127 project prior to flight.

Despite the success of the P.1127 flight program, the British Royal Air Force did not

consider the aircraft as a serious strike aircraft, citing an unacceptably small payload

capability and low engine thrust. Aggravating the lack of interest, in March 1961 NATO

requested proposals for a new V/STOL close-support fighter with supersonic speed

capability. The Hawker design team responded with the P.1154, a configuration with

twice the thrust, twice the speed, twice the weight, and twice the performance of the

P.1127. While pursuing the P.1154, Hawker continued demonstrations of the subsonic

P.1127 and kept the program alive.

Langley chief test pilot Jack Reeder evaluated the P.1127 in 1962.
Langley Contributions to the AV-8

16 Boeing AV-8 Harrier

On June 13, 1962, Langley chief test pilot Jack Reeder became the first foreign pilot to

fly the P.1127. Despite the fact that he had never flown in the military service,

Reeder was vastly experienced, having flown over 177 different aircraft of which 7 were

V/STOL research aircraft. His V/STOL flight experience was unrivaled and Hawker

eagerly awaited his opinion of the P.1127. Reeder returned to the U.S. filled with enthusiasm for the P.1127 and he influenced many decision makers regarding the potential of

the aircraft for military applications.

The Labour government in the United Kingdom cancelled the P.1154 program and

instructed the frustrated Royal Air Force to accept an upgraded version of the subsonic

P.1127—the Harrier. But first, the P.1127 was developed into an interim version known

as the Kestrel. Nine Kestrel aircraft participated in a unique international collaboration

that was designed to assess the practicality of V/STOL operations in the field.

Contributions to the Kestrel Under the leadership of the MWDP, an agreement was signed in late 1961 by the United

States, the Federal Republic of (West) Germany, and the United Kingdom to test an

improved P.1127 concept in field conditions in the United Kingdom. Changes made to

the P.1127 to upgrade it into the Kestrel included a new engine with increased thrust, a

new swept wing with more fuel capacity than the P.1127 wing, a drooped horizontal tail,

and improved reaction controls. The flight-test evaluations began in 1965. At the end of

9 months of flight evaluations, the squadron pilots gave glowing reports about the flying

qualities of the Kestrel.

Jack Reeder was an active participant in the evaluation program, especially in discussions about required improvements in the Kestrel handling qualities. Following the

international flight program, Reeder persuaded officials to provide Langley with two

Kestrel aircraft for follow-on V/STOL research. Langley test pilots Lee H. Person, Jr.

and Perry L. Deal flew the Kestrels (designated XV-6A) at Langley under the leadership

of Reeder.

Contributions of the Kestrel flight tests at Langley had profound impact on the operational usage of this unique vehicle in both the powered-lift regime, as well as in conventional maneuvering flight. Extensive flight evaluations of the efficiency of existing

Kestrel instrument approach procedures led by researcher Samuel A. Morello identified

new methods to permit safer, more fuel-efficient approaches and landings. However, the

most valuable contribution made by the Langley team was the flight research and engineering development that permitted the rotatable nozzles to be deflected in maneuvering

flight, thereby providing unprecedented maneuvering for air-to-air combat.

In 1969, the Defense Department requested that Langley review and comment on a

report written by Dr. John Attinello, an engineer of the Institute of Defense Analyses,

that favorably discussed the potential of using thrust vectoring on P.1127-type aircraft to

enhance the maneuverability of fighters in air combat. Although the application of vectoring in forward flight (VIFF) was fundamentally attractive, considerable engineering

concern existed over potential control requirements, stability characteristics, and the

physical well being of the engine in such maneuvers.

The Langley team designed a flight-test program to develop and evaluate the VIFF concept with the Langley Kestrel. Person and Deal were assigned as project pilots and

Richard G. Culpepper was assigned as project engineer. Hawker was initially very skeptical and very concerned over the flight-test objectives, with a special concern expressed

over the internal air ducts leading to the reaction control “puffers” at the wingtips and
Langley Contributions to the AV-8

Boeing AV-8 Harrier 17

tail of the Kestrel. Operation of the reaction controls at high speeds could result in the

internal ducts bursting. There was also concern about handling problems, especially at

high angles of attack.

The initial flight trials were conducted in straight and level flight, with Person carefully

evaluating internal duct pressures, angle of attack, engine exhaust gas temperatures, and

handling qualities. The flight envelope was gradually opened up to 250 knots, then up to

450 knots, until the nozzles could be deflected from the horizontal (cruise) position

downward through 90 deg to the breaking stop position. In level flight, the deceleration

of the aircraft was extremely high and Person reasoned that the abrupt change in speed

could be used to force an enemy pilot to over shoot and become the target. The Kestrel

also experienced a nose-up trim change when VIFF was used, but forward stick could

be used to maintain attitude. During simulated air combat maneuvers, Person would

rotate the nozzles all the way down, roll the wings into the turn and create a very rapid,

very high decelerating turn. Other Langley pilots who chased the Kestrel in a Langley T38 aircraft (including Robert A. Champine, noted X-1 pilot) observed that the Kestrel

appeared to “turn a square corner” and added their enthusiasm to that of the test crew.

This initial exploration of VIFF was conducted by Langley from January 1970 to the

end of June 1970.

Following the completion of the flight trials of VIFF in 1970, attempts to obtain a more

modern Harrier aircraft for follow-on VIFF experimentation met with great disappointment because only six development batch Harriers were available, and all six were

heavily involved in development flying in the United Kingdom. Former astronaut

Neil A. Armstrong, then serving as Deputy Associate Administrator for Aeronautics at

NASA Headquarters, used his influence to obtain a British Harrier and have it modified

for VIFF research by NASA. A joint VIFF program between NASA and the Royal

Lee Person and Jack Reeder with the two Kestrel (XV-6A) aircraft assigned to Langley.
Langley Contributions to the AV-8

18 Boeing AV-8 Harrier

Aircraft Establishment was initiated in 1972, and flying in the United Kingdom continued through 1976. Results obtained in flight evaluations against a variety of highperformance adversary aircraft and analyses of evasive maneuvers provided by VIFF

against enemy ground-to-air and air-to-air missiles resulted in overwhelming support

for VIFF as a valuable tool for the AV-8 pilot.

As far as the U.S. Marine Corps is concerned, the engineering contribution of NASA

was invaluable in developing and proving the VIFF concept (ref. 1).

Other studies of the Kestrel included wind-tunnel tests of a large, powered model in the

Langley V/STOL Tunnel (later renamed the Langley 14- by 22-Foot Subsonic Tunnel)

by a team led by Richard J. Margason with the objective of establishing wind tunnel to

flight correlation. Although the test results were published in a NASA report, the flight

correlation effort was not undertaken (ref. 6).

Contributions to the AV-8 The U.S. Marine Corps has unquestionably been the strongest supporter of the Harrier

concept. Most aircraft development programs, however, are driven by politics, service

rivalries, and many factors other than technology. In the fall of 1972, the U.S. Navy

issued a request for proposals of the next generation V/STOL aircraft. Unfortunately,

the list of candidates did not include any further development of the Harrier. Instead, the

Navy favored the North American Rockwell XFV-12A supersonic fighter design. The

XFV-12A used a thrust augmentation scheme that diverted the total exhaust flow of the

main engine and ejected it through a venetian blind arrangement in the wings to give

vertical-lift capability. The concept was considered by many at Langley to be very risky

when compared with the proven Harrier approach, but the Navy was prepared to fully

fund the development of the aircraft and close out further development of the Harrier.

Two activities subsequently transpired that resulted in Langley contributions to the AV-8

program. First, Langley supported test and analysis of the XFV-12A. Second, Langley

contributed airfoil design methods and wind-tunnel databases that played a key role in

the development of the second-generation AV-8B.

Naval Air Systems Command requested Langley support for the XFV-12A Program.

This support included testing a free-flight model in the Langley Full-Scale Tunnel and a

spin model in the Langley 20-Foot Vertical Spin Tunnel and conducting a remarkable

hovering test evaluation of an XFV-12A prototype at the Langley Impact Dynamics

Research Facility (IDRF). This facility, previously known as the Langley Lunar Landing

Facility, had been used to train astronauts for the reduced gravity levels of the moon’s

environment. Interest in using the IDRF was stimulated by the difficulty of mounting the

XFV-12A airframe on a more conventional pedestal mount for the hover test.

The results of the free-flight model tests in 1974 in the Full-Scale Tunnel indicated that

the projected thrust augmentation for the XFV-12A was considerably less than

expected, and the thrust available for vertical flight was insufficient to permit poweredlift flights. Although the configuration flew well in conventional wing-borne flight, the

Langley team expressed grave concern over the deficient V/STOL capability of the freeflight model.

In early 1978, tethered hover tests of the full-scale XFV-12A on the IDRF were carried

out by a joint team of NASA, Navy, and Rockwell personnel. Richard G. Culpepper

served as the lead Langley engineer for the investigation. The IDRF had undergone major modifications to permit static and dynamic tethered hover tests for powered

V/STOL aircraft. During 6 months of tests, it became apparent that major deficiencies

existed in the XFV-12A for hovering flight, including marginal vertical thrust. Although
Langley Contributions to the AV-8

Boeing AV-8 Harrier 19

Langley researcher William Newsom with the XFV-12A free-flight

model with augmentor doors on wing and canard open.

XFV-12A aircraft mounted for tethered hover flights on

Langley Impact Dynamics Research Facility.
Langley Contributions to the AV-8

20 Boeing AV-8 Harrier

the augmentation of flow at the wing augmentors was as predicted, large losses in the

internal ducting and corners of the propulsion system seriously degraded the net thrust

to the extent that only 75 percent of the weight of the vehicle could be supported in

attempts to hover. The results of the tests at Langley influenced the Navy’s decision to

cancel the XFV-12A Program.

Meanwhile, faced with the potential end of the Harrier program, McDonnell Douglas

and its partners launched a major redesign effort to provide a significant improvement in

the V/STOL capability of the AV-8A. McDonnell Douglas engineers drew on two fundamental research efforts at Langley to assist them in redesigning the AV-8A into the

AV-8B. Under the leadership of Richard E. Kuhn, Langley researchers in the Langley

V/STOL Tunnel conducted systematic wind-tunnel studies of the aerodynamic interactions that occur between rotatable fuselage-mounted nozzles and a high wing with a

trailing-edge flap. The test variables included a range of geometric relationships

between these components and showed that the resulting total lift for an aircraft similar

to the Harrier could be significantly impacted (both favorably and unfavorably) by the

positioning of these elements. Drawing on this database, the McDonnell Douglas engineers arrived at the current AV-8B wing-nozzle-flap configuration, which resulted in an

increase of more than 6,000 lb of lift beyond that produced by the AV-8A arrangement.

In addition, McDonnell Douglas used methods that had matured from the research of

Dr. Richard T. Whitcomb for supercritical airfoils. The resulting AV-8B wing design has

a thicker wing with better performance at high speeds, better fuel consumption, and provides an increase in internal fuel capacity of over 40 percent.

After the decision was made by NASA Headquarters in 1973 to consolidate all V/STOL

research under the leadership of the NASA Ames Research Center, additional windtunnel and V/STOL flight research on the Harrier was conducted by Ames, and close

NASA involvement in the AV-8 Program continues today.

Langley continues to support the program in areas unique to Langley expertise and

facilities. For example, spin tunnel tests were conducted at Langley for the AV-8B in

1984, as the external configuration, armament, and other important factors changed in

the AV-8 fleet.
Highlights of Research by Langley for the C-17

Boeing C-17 Globemaster III 21

Boeing C-17 Globemaster III

HIGHLIGHTS OF RESEARCH BY LANGLEY FOR THE C-17

1. Langley conceived, researched, and developed an externally blown flap concept that

permits the C-17 to make slow, steep approaches with heavy payloads.

2. The C-17 uses supercritical wing technology, developed at Langley, which enhances

range, cruising speed, and fuel efficiency at transonic cruise conditions.

3. The C-17 employs winglets, conceived and developed at Langley, for better cruise

efficiency with a reduced wing span.

4. Fly-by-wire technology, used by the C-17 as a lighter weight replacement for a

hydraulic control system, was initially researched at Langley.

5. Research led by Langley on the development of composite materials enabled the

C-17 to employ advanced composites for significant weight savings.

6. Langley conducted flutter clearance tests for the C-17 wing and winglet configuration.

7. Langley conducted fundamental research on deep-stall characteristics of T-tail aircraft, providing McDonnell Douglas with background for the development of the

C-17 angle-of-attack limiting system.

SPECIFICATIONS

Manufacturer

Boeing

Date in service

January 1995

Type

Transport

Crew

Three

Engine

Pratt & Whitney F117-PW100 turbofan

USER

U.S. Air Force

DIMENSIONS

Wingspan. . . . . . . . . . . 169.8 ft

Length . . . . . . . . . . . . . 174.0 ft

Height . . . . . . . . . . . . . . 55.1 ft

Wing area. . . . . . . . . 3,800 sq ft

WEIGHT

Empty . . . . . . . . . . . 277,000 lb

Max take-off . . . . . . 585,000 lb

PERFORMANCE

Max speed . . . . . Mach number

of 0.77

Range. . . . . . . . . . . . 4,741 n mi
Highlights of Research by Langley for the C-17

22 Boeing C-17 Globemaster III

The C-17 is the newest airlift aircraft to enter the Air Force inventory. The C-17 is capable of rapid strategic delivery of troops and all types of cargo to main operating bases or

directly to forward bases in the deployment area. The aircraft is also able to perform theater airlift missions when required. Using advanced aerodynamics and an innovative

NASA powered-lift concept, the C-17 combines the load carrying capacity of the C-5

with the short takeoff and landing performance of the C-130. McDonnell Douglas was

recognized in 1994 for the innovative design of the C-17 with the prestigious Collier

Trophy, which is awarded annually for the greatest achievement in aviation in the

United States.

Fundamental and applied aeronautics research conducted at Langley in the areas of

advanced high-lift systems, aerodynamics, advanced composites, and aeroelasticity contributed to the success of the C-17. Decades of Langley research efforts had conceived,

developed, and matured emerging concepts and design guidelines that helped

McDonnell Douglas produce this outstanding military transport. Langley facilities associated with research for the C-17 included the 30- by 60-Foot (Full-Scale) Tunnel, the

300-MPH 7- by 10-Foot Tunnel, the 16-Foot Transonic Dynamics Tunnel, the 8-Foot

Transonic Pressure Tunnel, piloted simulators, and the Structures and Materials

Laboratory.

In an acknowledgement of Langley’s involvement in the C-17, McDonnell Douglas and

the Air Force brought a C-17 to Langley on May 24, 1996, for a special ceremony to

thank the employees for their contributions to the design of the C-17.
Langley Contributions to the C-17

Boeing C-17 Globemaster III 23

LANGLEY CONTRIBUTIONS TO THE C-17

The CX Competition In the late 1970’s, the U.S. military recognized a growing demand for rapid deployment

of military forces and equipment that would exceed the capabilities of the existing

C-141, C-5, and C-130 fleets. Early in 1980, the Department of Defense (DOD) issued a

request for proposals (RFP) for a new Cargo Experimental (CX) Program. Boeing,

Lockheed, and McDonnell Douglas submitted variants of civil transports, derivatives of

the prototype YC-14 and YC-15 aircraft, and completely new aircraft in response to the

RFP. In August 1981, the Air Force announced that it had selected the Douglas Aircraft

Company Division of McDonnell Douglas to develop the CX, now known as the C-17.

Langley’s contributions to the development of the C-17 included years of consultation

and cooperative research with the Douglas team, providing unique test facilities, and

several innovative technological concepts.

The Externally Blown Flap 

Concept

The specifications for the C-17 transport required advanced concepts for superior short

takeoff and landing (STOL) performance. As a result of Langley research on powered

high-lift systems for over 35 years, the innovative externally blown flap (EBF) concept

had matured to the point that it could be incorporated in the C-17 transport. The EBF

enables the C-17 to make slow, steep approaches with heavy cargo loads to touch down

precisely on the spot desired on limited runway surfaces. Because of this technology

that was developed by Langley, the C-17 can carry the same loads as a C-5 and use the

same airfields as a C-130.

John P. Campbell of Langley conceived the EBF concept in the mid-1950’s as a relatively simple approach to augment wing lift for low-speed operations. In this concept,

the exhaust from pod-mounted engines impinges directly on conventional slotted flaps

and is deflected downward to augment the wing lift. The magnitude of lift augmentation

is extremely large, and the resulting lift can be as much as twice the value for a conventional aircraft. However, no serious consideration was given to the EBF concept initially

because of the severe high-temperature impingement on the wing and flap surfaces from

the turbojet (no bypass or fan flow) engines used at that time. Also, the relatively small

mass flow from such engines was a limiting factor for lift augmentation. In addition,

considerable concern was expressed over potential control problems in the event that an

engine became inoperative during flight at low speeds with high-power settings. With

the advent of turbofan engines, however, the efflux from the engines was relatively cool,

and large quantities of air became available for increased airflow through the flaps. The

turbofan engine, therefore, provided the breakthrough mechanism that permitted

Langley researchers to evolve and mature the applications of the EBF concept.

At Langley, extensive wind-tunnel tests in the Langley 30- by 60-Foot (Full-Scale)

Tunnel and the Langley 300-MPH 7- by 10-Foot Tunnel explored the fundamental liftaugmentation capability of the EBF for various wing-engine nacelle-flap combinations.

These tests defined the optimum wing and flap geometries for application to aircraft

configurations. Led by Joseph L. Johnson, Jr., a team of researchers in the Full-Scale

Tunnel studied the aerodynamic performance of two- and four-engine EBF transport

configurations. The scope of their research included detailed studies of projected aircraft

performance, potential control problems and solutions, and design guidelines for the

general geometric layout of the aircraft. The advantage of using a T-tail empennage configuration was identified as a desirable approach to avoid the large local downwash

angles experienced at conventional tail locations due to the increased wing circulation
Langley Contributions to the C-17

24 Boeing C-17 Globemaster III

produced by the EBF concept. The engine-out control issue was addressed and solved

by defining the vertical tail and rudder size required to maintain directional control.

Dynamically scaled models of transport configurations vividly demonstrated the highlift potential of the EBF concept, while exhibiting satisfactory stability and control characteristics, in free-flight wind-tunnel tests. Aerodynamic data generated by these studies

were then used for piloted-simulator studies of EBF transports at Langley, during which

more realistic evaluations of the handling qualities could be conducted and flight control

systems could be configured. Throughout the years that the EBF concept developed and

matured, Langley researchers coordinated with U.S. industry and DOD. Langley

provided briefings and invaluable technical reports that summarized the findings of

the research studies and the revolutionary capability offered by this new concept in

aeronautics.

In the late 1960’s, the progress on the EBF concept had advanced considerably, and

most of the major issues had been adequately addressed and resolved. The concept was

now ready for flight evaluation on an actual aircraft. Langley advocated for a special

flight demonstrator program and conducted several studies of the feasibility of modifying existing aircraft as appropriate test beds. The Douglas A3 Skywarrior twin-engine,

high-wing aircraft operated by the U.S. Navy appeared to be a desirable option; however, a new DOD program known as the Advanced Tactical Transport Program superseded the Langley plans.

The YC-15 In 1972, the Air Force issued a request for proposals (RFP) for an Advanced Medium

STOL Transport (AMST) that would ultimately replace the C-130 tactical transport.

The program emphasized innovative technologies and the capability of conducting

STOL operations from 2,000-ft runways. Boeing and McDonnell Douglas were each

Langley researcher John P. Campbell (l) and Gerald G. Kayten (r) of NASA Headquarters

inspect a free-flight model of an EBF configuration in the Langley Full-Scale Tunnel.
Langley Contributions to the C-17

Boeing C-17 Globemaster III 25

awarded preliminary design contracts for the construction and testing of two transport

prototypes, respectively designated YC-14 and YC-15.

Boeing based their YC-14 design on another powered-lift concept known as upper surface blowing (USB), which had also been developed at Langley in efforts led by Joseph

Johnson and Oran W. Nicks, Deputy Director of Langley. In the USB concept, the

engines were mounted so that the exhaust spread over the upper surface of the wing for

enhanced circulation and lift augmentation in STOL operations.

McDonnell Douglas used the EBF concept with a four-engine configuration and large

double-slotted flaps that extended over 75 percent of the total span for the YC-15 prototypes. The first of two YC-15 prototypes made its first flight on August 26, 1975, and

was joined by the second prototype in December of that year. The YC-15 demonstrated

exceptional STOL performance in its flight-test program with an approach speed of only

98 mph and a field length of 2,000 ft at a landing weight of 150,000 lb.

During the flight-test program for the YC-15, Langley researchers participated in evaluations and analysis of STOL capabilities, including an assessment of lift augmentation

in ground effect. In addition to participating in the flight tests of the YC-15, Langley

conducted a cooperative wind-tunnel test in the Langley 8-Foot Transonic Pressure Tunnel to evaluate the effectiveness of the emerging winglet concept, which was developed

by Langley, on the YC-15 configuration. Dr. Richard T. Whitcomb’s winglet designs are

small, wing-like vertical surfaces located at each wingtip that enable an aircraft to fly

with greater efficiency. Winglets are strategically located at the wingtip to produce a forward force on the aircraft, similar in many respects to the sail on a sailboat.

Although the YC-15 was never placed into production, the experiences gained by

McDonnell Douglas in advanced wing design (supercritical airfoil and winglets), the

EBF concept, and advanced controls for STOL operations gave the company confidence

in future applications of these technologies to the C-17.

One of the McDonnell Douglas YC-15 prototypes in flight.

YC-15 model in the Langley 8-Foot Transonic Pressure

Tunnel for an evaluation of winglets.
Langley Contributions to the C-17

26 Boeing C-17 Globemaster III

The C-17 Supercritical Wing, 

Winglets, and Aerodynamic 

Studies

The YC-15 was the first military transport to use supercritical wings, a major innovative

technology conceived and developed through wind-tunnel research by Richard

Whitcomb at Langley. Whitcomb’s supercritical wings incorporate advanced airfoils

that enhance the range, cruising speed, and fuel efficiency of aircraft by producing

weaker upper-surface shock waves, thereby creating less drag and permitting higher

efficiency. McDonnell Douglas subsequently incorporated supercritical wing technology in the C-17 design.

Whitcomb’s brilliant development of the winglet concept was another product of

research at Langley that was ideally suited for the C-17. The C-17 is a large aircraft with

a relatively small wing. The wingspan of the C-17 was dictated by an Air Force requirement for three aircraft to maneuver on a ramp measuring 90 m by 122 m that is connected by a 15-m-wide taxiway. The aerodynamic contribution of the winglets permits

the C-17 to employ a shorter wing span while retaining the efficiency of a larger wing

span. The C-17 winglets also employ supercritical airfoil sections.

The successful application of winglets to the C-17 also required consideration and analysis of the flutter characteristics of the wing-winglet combination. This area was of particular concern because flow separation in the wing-winglet juncture could provide an

aggravating mechanism that might lower the flutter speed to within the flight envelope

of the C-17. Led by Charles L. Ruhlin, a Langley, McDonnell Douglas, and Air Force

team conducted flutter tests on the C-17 wing-winglet configuration in the Langley

16-Foot Transonic Dynamics Tunnel and successfully cleared the aircraft for flight tests.

Several cooperative wind-tunnel test studies were conducted by McDonnell Douglas

and Langley in the National Transonic Facility (NTF) at the Langley Research Center to

assess and optimize the cruise aerodynamic performance of the C-17. The unique capability of the NTF to more properly simulate full-scale aerodynamic flight conditions has

been an extremely valuable contribution to the program.

Semispan model for the C-17 wing-winglet configuration in the

Langley 16-Foot Transonic Dynamics Tunnel for flutter tests.

C-17 model mounted in the National Transonic 

Facility at Langley for aerodynamic studies.
Langley Contributions to the C-17

Boeing C-17 Globemaster III 27

Composite Materials The initiation of the Aircraft Energy Efficiency (ACEE) Program by NASA in 1976 in

response to the energy crisis accelerated the development of concepts to improve the

efficiency of advanced aircraft. New methods of producing unique, lightweight materials were one of the major thrusts of the ACEE Program, with emphasis on durable composite materials for aircraft structures. The Structures Division at Langley played a key

role in developing the technology, which was ultimately incorporated on several components of the C-17. One of the most valuable Langley contributions in the ACEE Program was the development of graphite-epoxy upper aft rudders for the DC-10. The

rudders have accumulated over 500,000 flight hours since they were introduced into regular airline service in 1976, thereby providing extensive experience for applications to

other aircraft, including the C-17.

Several major components of the C-17 are made of advanced composites (ailerons, rudders, elevators, vertical and horizontal stabilizers, flap hinge fairings, main landing gear

pod panels, and winglets). Over 16,000 lb of composites are incorporated in the design,

with composites accounting for about 8 percent of the structure.

Fly-by-Wire Control System The extensive database and literature produced by pioneering research at Langley on

fly-by-wire flight control systems and handling qualities of STOL transports provided

McDonnell Douglas with a rich source of information in the development of the C-17

flight control system. Although not directly involved in this facet of the C-17 development program, Langley contributed fundamental research information that helped build

the confidence and risk reduction required for the application of the sophisticated C-17

systems.

Avoiding the Deep Stall The T-tail empennage configuration offers significant aerodynamic advantages over

conventional designs. The relatively high location of the horizontal tail places the tail in

a relatively undisturbed airflow at normal cruise conditions, thereby maximizing the

contribution of the tail to stability and control. Many military and civil design teams

have adopted this tail configuration very successfully. However, the application of the

T-tail requires consideration of critical aerodynamic factors—especially an analysis in

wind-tunnel tests to ensure satisfactory handling characteristics at extreme pitch attitudes. At high angles of attack associated with wing stall, the low-energy wake of the

stalled wing can impinge on the horizontal tail and result in a loss of longitudinal stability (pitch up) and markedly reduced longitudinal control effectiveness. As a result of

these flow phenomena, the angle of attack can increase to a deep-stall condition, in

which the aircraft enters a stable but uncontrollable trim point with a very high rate of

descent.

In the early 1960’s, a British BAC 111 T-tail transport experienced a fatal accident in

which the aircraft entered a deep stall and descended in an uncontrollable condition at a

very high rate of descent with an almost horizontal fuselage attitude until impact.

Worldwide interest in the causes of this accident resulted in a research program at the

Langley Research Center on the behavior of T-tail configurations at high angles of

attack. Under the leadership of Robert T. Taylor and Martin T. Moul, extensive windtunnel and piloted-simulator studies were conducted to determine the aerodynamic

characteristics associated with deep-stall trim conditions and to develop design methods

and pilot techniques to recover from such conditions. A large number of aircraft configurations were studied in the Langley 7- by 10-Foot High-Speed Tunnel, with an emphasis on designs with aft-fuselage-mounted engine nacelles. Studies at Langley on the
Langley Contributions to the C-17

28 Boeing C-17 Globemaster III

T-tail deep-stall phenomenon provided a valuable database that has been used extensively in the design of numerous T-tail civil and military transport configurations. Perhaps the most valuable contribution of this work is the guidance and approach it

suggests to the designer during early wind-tunnel tests and configuration layout.

The C-17 design team was very familiar with the existing NASA database and design

procedures for avoiding the deep-stall problem. The quadruple redundant digital fly-bywire flight control system of the C-17 provides automatic limiting of angle of attack for

high-angle-of-attack conditions, thereby preventing any tendency of the aircraft to enter

an uncontrollable deep-stall condition.

Recognition Visit On May 24, 1996, McDonnell Douglas and the Air Force brought a C-17 of the Air

Mobility Command from Charleston Air Force Base, S.C., to Langley as a gesture of

thanks to Langley and its employees for their contributions to the design of the new military jet transport. The visit and formal ceremony acknowledged the contributions of all

four NASA Aeronautics Centers (Langley, Ames, Dryden, and Glenn) to the design and

development of the C-17. The NASA research contributions cited by the visitors

included the areas of powered-lift systems, short takeoff and landing control systems,

head-up display technology, supercritical wing and winglet, fly-by-wire systems, engine

technologies, and composite materials.

C-17 in front of the hangar during a visit at Langley on May 24, 1996.
Highlights of Research by Langley for the F/A-18

Boeing F/A-18 Hornet 29

Boeing F/A-18 Hornet

HIGHLIGHTS OF RESEARCH BY LANGLEY FOR THE F/A-18

1. At the request of industry and the military, Langley participated in reviews and

assessments from the YF-17 prototype program to the development of F/A-18E/F.

2. Langley provided wind-tunnel research on wing leading- and trailing-edge flap technology for transonic maneuver optimization.

3. Langley contributed to cooperative studies of vortex lift with McDonnell Douglas

and Northrop and participated in the selection of the wing leading-edge extension

(LEX) shapes for all variants of the F/A-18.

4. Langley provided a solution (porous wing doors) to a severe wing-drop tendency for

the F/A-18E/F, thereby helping to avoid potential termination of the aircraft

program.

5. Langley helped solve numerous F/A-18 developmental challenges including

• Cruise performance

• Flutter clearance

• High-angle-of-attack stability and control

• Recovery from unusual out-of-control conditions

6. Langley led the NASA High-Angle-of-Attack Technology Program, which provided

valuable information on F/A-18 characteristics and design methodology for future

fighters.

SPECIFICATIONS

Manufacturer

Boeing and Northrop Grumman

Date in service

1983

Type

Multirole fighter-attack aircraft

Crew

One or two

Engine

F-18C . . . . . . .General Electric

F404-GE-402

F-18E . . . . . . .General Electric

F414-GE-400

USERS

U.S. Navy, U.S. Marine Corps, 

Canada, Australia, Spain, Kuwait, 

Switzerland, Finland, and 

Malaysia

DIMENSIONS

Wingspan

F-18C . . . . . . . . . . . . . .40.4 ft

F-18E . . . . . . . . . . . . . .44.9 ft

Length

F-18C . . . . . . . . . . . . . .56.0 ft

F-18E . . . . . . . . . . . . . .60.3 ft

Height

F-18C . . . . . . . . . . . . . .15.3 ft

F-18E . . . . . . . . . . . . . .16.0 ft

Wing area

F-18C . . . . . . . . . . 400.0 sq ft

F-18E . . . . . . . . . . 500.0 sq ft

WEIGHT

Empty

F-18C . . . . . . . . . . . 23,407 lb

F-18E . . . . . . . . . . . 30,500 lb

Gross

F-18C . . . . . . . . . . . 51,900 lb

F-18E . . . . . . . . . . . 66,000 lb

PERFORMANCE

Max speed . . . . . . . . above Mach 

number of 1.8
Highlights of Research by Langley for the F/A-18

30 Boeing F/A-18 Hornet

The Langley Research Center has been an active participant in the development

of the F/A-18 series of aircraft for over 25 years, including contributions to the YF-17,

F/A-18A, and the F/A-18E/F. With the exception of the F-111, no other fighter aircraft

has been the subject of as many Langley wind-tunnel studies and analytical investigations. Working closely with Boeing (formerly McDonnell Douglas) and Northrop

Grumman (formerly Northrop), Langley has contributed to aerodynamic performance,

computational fluid dynamics, high-angle-of-attack stability and control, and aeroelasticity. Langley facilities used in the development of the F-18 included the 30- by

60-Foot (Full-Scale) Tunnel, the 12-Foot Low-Speed Tunnel, the 20-Foot Vertical Spin

Tunnel, the 8-Foot Transonic Pressure Tunnel, the 16-Foot Transonic Tunnel, the Jet

Exit Test Facility, the 16-Foot Transonic Dynamics Tunnel, the 7- by 10-Foot HighSpeed Tunnel, the 14- by 22-Foot Subsonic Tunnel, the Differential Maneuvering Simulator, radio-controlled drop models, and computational facilities.

Research contributions by Langley for the F/A-18 have increased lift for aggressive

maneuvering, improved cruise performance, insured a high degree of spin resistance,

provided flutter clearance, and enabled prompt recovery from out-of-control conditions.

Recently, one of the most significant Langley contributions was providing a solution to

an uncommanded wing-drop characteristic exhibited by the F/A-18E/F. Boeing was

awarded the Collier Trophy in 1999 in recognition of the accomplishments in the

F/A-18E/F program.

Langley provided the lead advocacy and technical leadership for a highly successful

NASA High-Angle-Of-Attack Technology Program based on the F/A-18 configuration.

The program aggressively accelerated progress in design methods for aerodynamics,

flight controls, thrust vectoring, alleviation of empennage buffet, and test techniques.

Extensive documentation and analysis of F/A-18 characteristics were significant byproducts of the program.
Langley Contributions to the F/A-18

Boeing F/A-18 Hornet 31

LANGLEY CONTRIBUTIONS TO THE F/A-18

Vortex Lift and Maneuvering 

Flaps

In the early 1960’s, the Northrop Company noticed an improvement in the maximum lift

of the F-5 aircraft because of a small flap actuator fairing that extended the wing root

leading edge. This phenomenon spurred interest in the effects of inboard vortex

flows and led to a cooperative NASA and Northrop study, which was conducted in the

Langley 7- by 10-Foot High-Speed Tunnel with a group led by Edward C. Polhamus.

The cooperative study of hybrid wings centered on the use of relatively large, highly

swept wing extensions at the wing-fuselage intersection, which promoted strong beneficial vortex-flow effects. The scope of the study included parametric studies to maximize

the lift- and stability-enhancing effects of the wing extension concept, which became

known at Northrop as the leading-edge extension (LEX). Studies were also directed at

cambering the leading edge of the LEX to suppress the vortex at low angles of attack,

and thereby minimize drag at cruise conditions. Northrop applied a large highly swept

LEX to the YF-17 prototype aircraft to enhance lift and stabilize the flow over the YF17 main wing at high angles of attack.

From these initial cooperative studies with Northrop, Polhamus and his associates put

together a world-class vortex-lift research program that became internationally recognized for its experimental database, analytical procedures, and aircraft applications. In

addition to Polhamus, key members of this team included Linwood W. McKinney,

Edward J. Ray, William P. Henderson, John E. Lamar, and James M. Luckring. Their

extraordinary research into the fundamentals and applications of vortex flows placed the

Langley Research Center in an excellent position to aid the U.S. industry in the design

of highly maneuverable advanced fighters. This experienced pool of experts would subsequently provide invaluable guidance and analysis to industry design teams in the

development of the F-16 for the Air Force and the F/A-18 for the Navy.

F/A-18 with wing leading-edge flaps deflected

and LEX vortices made visible by condensation.
Langley Contributions to the F/A-18

32 Boeing F/A-18 Hornet

In Vietnam, the lack of maneuverability of U.S. fighters at transonic speeds provided

key advantages to nimble enemy fighters. Industry, the Department of Defense (DOD),

and NASA were all stimulated to sponsor research to achieve unprecedented transonic

maneuverability while maintaining excellent handling qualities. Langley researchers,

under the leadership of Polhamus, conducted studies in the 7- by 10-Foot High-Speed

Tunnel to obtain near optimum aerodynamic maneuver performance for wings, including the use of fixed and variable camber concepts. Some of the earliest systematic windtunnel tests were conducted by the group to determine the most effective geometries for

wing leading- and trailing-edge flaps. In addition to tests of aerodynamic performance

and stability and control, buffet studies were conducted to understand and develop

methodologies for the prediction and minimization of undesirable buffet characteristics.

The program was closely coordinated with flight tests of actual high-performance fighters at the NASA Dryden Flight Research Center. Flight evaluations of the effects of

maneuver flaps on a YF-17 were also later conducted in the Dryden program.

Numerous discussions with Polhamus and his staff provided valuable guidance to the

Northrop design team and the McDonnell Douglas team for the subsequent F/A-18

design. The insight and understanding provided by the broad database from Langley

tests permitted development of the extremely effective leading- and trailing-edge flaps

used by the YF-17 and the F/A-18. The F/A-18 and similar high-performance fighters

use specific, computer-controlled schedules of flap deflection with Mach number and

angle of attack for superior maneuverability throughout the flight envelope.

Development of the YF-17 On January 6, 1972, the Air Force issued a request for proposals (RFP) for a Lightweight Fighter (LWF) Program. In March 1972, the Langley Research Center was

requested by DOD to participate in assessments and supporting tests of the competing

YF-16 and YF-17 designs for the LWF. Langley researchers became members of DOD

source evaluation teams to assess and check technical claims by each of the contractors.

The sponsoring LWF Program Office requested that certain services of Langley be made

available on an equal basis to the two competing teams. This remarkable arrangement

provided each team with analysis and support if they desired.

Northrop placed a high priority on superior high-angle-of-attack characteristics and a

high degree of inherent spin resistance for the YF-17. The company had also placed priorities in these areas during the development of the F-5 and T-38 aircraft, which had

become known for outstanding resistance to inadvertent spins. Langley support was

therefore requested for tests in the 30- by 60-Foot (Full-Scale) Tunnel and the 20-Foot

Vertical Spin Tunnel.

To provide superior handling qualities at high angles of attack for fighter aircraft,

Northrop provided the airframe with the required levels of aerodynamic stability and

control characteristics without artificially limiting the flight envelope with the flight

control system. This approach proved to be highly successful for the YF-17 and has

been adopted by McDonnell Douglas (now Boeing) and used in all variants of

the F/A-18 aircraft.

Researcher Sue B. Grafton conducted exhaustive tests in the Full-Scale Tunnel of the

YF-17 configuration at high angles of attack in 1973. The results of the Langley tests

revealed that Northrop had done an outstanding job in configuring the YF-17 design.

The integration of the large LEX surfaces and the placement of the twin vertical tails

provided exceptional tail effectiveness at high angles of attack. The small strakes added

to the forward fuselage nose by Northrop resulted in extremely high directional stability

at high angles of attack. Free-flight tests of the YF-17 model in the Full-Scale Tunnel
Langley Contributions to the F/A-18

Boeing F/A-18 Hornet 33

confirmed the excellent flying characteristics predicted by the wind-tunnel data and provided Northrop with highly positive predictions for upcoming flight tests of the two

YF-17 prototypes at Edwards Air Force Base. The wind-tunnel data also formed the

basis for piloted simulator studies at Langley and Northrop that helped Northrop design

the flight control system for critical high-angle-of-attack conditions.

Spin and recovery tests in the Spin Tunnel also provided positive results for the YF-17.

The scope of the tests in the Spin Tunnel was relatively broad for the fast-paced LWF

Program and included the determination of the size of the emergency spin recovery

parachute that would be required for flight tests. The results of the Spin Tunnel tests

showed that the YF-17 would have remarkably good spin and recovery characteristics.

In fact, the YF-17’s characteristics were the best noted for any fighter configuration to

that time.

Although not specifically requested by the Air Force, Langley had already conducted

Air Force approved studies of the high-angle-of-attack characteristics of the YF-16 in

the Langley Differential Maneuvering Simulator (DMS) and approval was given to conduct similar studies of the YF-17. Under the leadership of Langley researchers Luat T.

Nguyen and William P. Gilbert, extensive studies were conducted in the DMS to verify

the impressive behavior predicted by the wind-tunnel and free-flight model tests for

more realistic air combat conditions. In addition, the simulation was used to refine certain elements of the flight control system for high-angle-of-attack conditions. The

results of the simulator investigation showed the YF-17 to be highly maneuverable and

departure resistant throughout the operational angle-of-attack range and beyond maximum lift.

Project engineer Sue Grafton with the free-flight model of the YF-17 in 1973.
Langley Contributions to the F/A-18

34 Boeing F/A-18 Hornet

A YF-17 prototype in flight with the open

slots in the LEX adjacent to the fuselage.

YF-17 model in the Langley 8-Foot Transonic

Pressure Tunnel for drag assessment studies.
F/A-18A to F/A-18D

Boeing F/A-18 Hornet 35

The Langley predictions for the YF-17 behavior were subsequently confirmed in 1974

when two YF-17 prototypes began flight evaluations at Edwards Air Force Base. Handling characteristics at high angles of attack were excellent. The YF-17 could achieve

angles of attack of up to 34 deg in level flight and 63 deg could be reached in a zoom

climb. The aircraft remained controllable at indicated airspeeds down to 20 knots.

Northrop consequently claimed that their lightweight fighter contender had no angle-ofattack limitations, no control limitations, and no departure tendencies within the flight

envelope used for the evaluation.

Langley researchers conducted a cruise-drag test of the YF-17 in the Langley 8-Foot

Transonic Pressure Tunnel in 1973. The test was initiated when Northrop questioned the

high transonic drag levels predicted by the Air Force, which were based on results from

other wind tunnels. The Air Force agreed that an independent NASA analysis would be

appropriate and requested the test.

Langley researchers found that their results agreed with the Air Force predictions.

Researchers then identified the major contributors to drag and provided recommendations to reduce it. Dr. Richard T. Whitcomb reviewed the YF-17 drag results and concluded that the wing design was the major factor in the unexpected drag levels.

Whitcomb’s suggestion for a wing redesign to solve the problem was unacceptable to

Northrop.

F/A-18A TO F/A-18D

Development of the F/A-18 In April 1974, the LWF Program changed from a technology demonstration program to

a competition for an Air Force Air Combat Fighter (ACF), and the flight-test programs

for the YF-16 and YF-17 were rushed through in a few months instead of the planned

2 years. On January 13, 1975, the Air Force announced that the General Dynamics

YF-16 would be the new ACF. Congress decreed that the Navy adopt a derivative of one

of the LWF designs as the new Naval Air Combat Fighter to complement the F-14. On

May 2, 1975, the Navy announced that the YF-17 design would form the basis of their

new F/A-18 fighter-attack aircraft. Northrop, inexperienced in the design of naval fighters, teamed with McDonnell Douglas, which had extensive experience with a highly

successful line of naval aircraft, including the F-4 Phantom. McDonnell Douglas

became the prime contractor for the F/A-18 with Northrop the prime subcontractor.

The formidable task of converting the land-based YF-17 lightweight day fighter into an

all-weather fighter-attack aircraft capable of carrier operations with heavy ordnance

loads required significant changes from the earlier configuration. Structural strengthening and a new landing gear design were required for catapult launches and arrested landings. The aircraft gross weight rapidly grew from 23,000 lb for the YF-17 to a projected

weight over 33,000 lb.

The required approach speeds for carrier landings resulted in modifications to the wing

and LEX surfaces of the YF-17 configuration to provide more lift. McDonnell Douglas

consulted the Langley research staff, and several individuals participated in the analysis

of wind-tunnel tests that had been conducted at NASA Ames Research Center and

McDonnell Douglas facilities. As a result of the analysis, changes were made to the aircraft configuration. The geometric shape of the YF-17 LEX was extended farther forward on the fuselage and the plan view of the LEX was modified to produce additional

lift while retaining the good high-angle-of-attack characteristics exhibited by the YF-17.
F/A-18A to F/A-18D

36 Boeing F/A-18 Hornet

The deflections of the wing leading- and trailing-edge flaps were increased and the ailerons were programmed to droop in low-speed flight to augment lift. Finally, a “snag” or

discontinuity was added to the leading edges of both the wing and horizontal tails to

provide more lift.

Formal Navy requests for specific NASA studies in support of the evolving F/A-18 configuration were received and accepted by Langley. The excellent correlation of Langley

predictions for high-angle-of-attack and spin characteristics of the YF-17 prompted the

Navy to request the full suite of tests at Langley for these characteristics. A request for

tests in the Spin Tunnel and the Full-Scale Tunnel and helicopter drop models was

received in late 1976.

The first preproduction F/A-18 made its first flight on November 18, 1978, and entered

the initial phases of flight tests at the Patuxent River Naval Air Station in Maryland. The

preproduction flight-test program lasted from January 1979 to October 1982, and the

Langley staff was called on to help solve several critical developmental problems.

Cruise Drag Initial results from flight evaluations at Patuxent River in 1979 indicated that the cruise

performance of the F/A-18 was significantly below expectations, with a shortfall of

about 12 percent in cruise range. The performance deficiency became a weapon for

those who sought the termination of the F/A-18 Program. A number of reasons for the

poor performance were identified. Modifications to the engines, computer-controlled

schedules for the deflection of leading- and trailing-edge flaps, and other changes

reduced the cruise range deficit to about 8 percent, but aerodynamic drag remained a

problem.

In response to this critical threat to the program, a Navy and NASA F/A-18 working

group was formed in late 1979. The NASA members were all Langley personnel led by

researchers Richard Whitcomb, Edward Polhamus, and William J. Alford, Jr. With the

addition of members from the Navy, McDonnell Douglas, and Northrop, the group

totaled about 20 participants. After consideration of several approaches to reduce the

drag of the aircraft, the group recommended wind-tunnel and flight studies of modifications to several configuration features. Modifications included increasing the wing leading-edge radius, variations in the LEX camber, and filling in the slots in the LEXfuselage juncture. The Langley members identified the slots as a particularly undesirable feature with potentially high drag characteristics. Tests with favorable results were

conducted in the Langley 8-Foot Transonic Pressure Tunnel in early 1980. These

changes were implemented on the F/A-18 test aircraft at Patuxent River where they

were found to favorably increase the cruise range of the aircraft. The impact of filling in

the LEX slot on high-angle-of-attack characteristics was found to be acceptable in additional tests at Langley and F/A-18 flight tests.

High-Angle-Of-Attack, Spin, 

and Spin Recovery 

Characteristics

Langley responded to the Navy’s request for stall-spin tests in support of the F/A-18

with spin tunnel tests (1978), free-flight model tests (1978), and drop-model tests

(1979). The results of the Langley spin tunnel and drop-model tests were very favorable.

The F/A-18 configuration was found to be extremely resistant to spins. (The pilot was

required to maintain prospin controls for over 20 sec to promote a spin.) When

spins were entered, recovery could be effected very quickly. In the spin tunnel tests, the

F/A-18 model demonstrated the best spin recovery characteristics of any modern U. S.

fighter (as had the YF-17 configuration). During the limited model tests for spins, the

phenomenon known as “falling leaf” was not encountered, but it became a problem in

operational usage as will be discussed in a later section.
F/A-18A to F/A-18D

Boeing F/A-18 Hornet 37

The F/A-18 free-flight model tests that were conducted in the Full-Scale Tunnel were

very controversial; however, the model tests subsequently proved to be a major contributor to the success of the F/A-18 development program.

As previously discussed, early high-angle-of-attack tests had been completed in other

NASA and McDonnell Douglas wind tunnels to tailor the geometry of the F/A-18 for

good flight characteristics. The removal of the stabilizing nose strakes that were on the

YF-17, which would have interfered with the radar performance on the F/A-18, and the

revision of LEX shape had been carefully analyzed and designed from these results.

When the Langley free-flight model underwent tests, the LEX and leading-edge flap

schedule had been defined for flight tests.

When the Langley model was tested, however, the results obtained with this particular

model indicated that the F/A-18 would exhibit a moderate yaw departure near maximum

lift. Although not a flight safety concern, this result would infringe on the precision

maneuverability of the aircraft. These undesirable results had been obtained at low

wind-tunnel test speeds with a relatively large model and were dismissed with skepticism by the engineering community as having been caused by erroneous scale effects.

In 1979, an F/A-18 test aircraft at Patuxent River suddenly and unexpectedly departed

controlled flight during a wind-up turn maneuver at high subsonic speeds. None of the

baseline wind-tunnel data predicted this characteristic, and the F/A-18 Program was

shocked by the event. The fact that the free-flight model had also exhibited such a trend

did not go unnoticed, and a joint NASA, Navy, and McDonnell Douglas team was

formed to seek solutions with the free-flight model at Langley. Following exhaustive

wind-tunnel tests in the Full-Scale Tunnel, the team recommended that the wing leading-edge flap deflection be increased from 25 deg to 34 deg at high angles of attack. Following the implementation of this recommendation on the test aircraft (via the flight

F/A-18 drop model prepared for flight in 1978.
F/A-18A to F/A-18D

38 Boeing F/A-18 Hornet

control computers), no more departures were experienced, and the flap deflection schedule was adopted for production F/A-18’s.

This was not the first time that results from large free-flight models in the Full-Scale

Tunnel had proven to accurately predict the flight behavior of an aircraft at high angles

of attack, despite the low speeds of the wind-tunnel tests. (See Langley Contributions to

the F-16, for example.)

The NASA High-Angle-OfAttack Technology ProgramThe emergence of a generation of highly maneuverable fighter aircraft such as the F-14,

F-15, F-16, and F-18 in the late 1970’s resulted in a new perspective on operating highperformance aircraft at high angles of attack. Previous U.S. military experience with aircraft such as the F-4 and A-7 during the Vietnam era had been tormented with unacceptably high accident losses of these aircraft from inadvertent departures and spins from

maneuvers at high angles of attack. Operational procedures required very careful and

precise pilot inputs at high angles of attack to avoid loss of control, and handbook

restrictions were placed on the operational use of angle of attack. With the advent of the

new generation of fighters, flight at high angles of attack became a common occurrence

and was no longer feared or avoided by pilots. Exploitation of high angles of attack provided the potential for new maneuvers and options for air combat tactics. These interests

resulted in several major programs within DOD, industry, and NASA to develop the

analysis and design methodologies for superior performance over an unlimited range of

angle of attack.

In the early 1980’s, NASA initiated a High-Angle-of-Attack Technology Program

(HATP) among the aeronautics research centers (Langley, Ames, Dryden, and Glenn).

The program included all the critical elements of high-angle-of-attack technology: aerodynamics, flight controls, handling qualities, stability and control, and the rapidly evolving area of thrust vectoring. In recognition of its extensive accomplishments in this field,

Langley was designated the technology lead center for the program, and Dryden was

designated the lead for flight research and operations. The Langley leader in the initial

phases of the program was William Gilbert, who was followed by Luat Nguyen in later

years.

The F/A-18A free-flight model during tests in the Langley 30- by 60-Foot Wind Tunnel in 1978.
F/A-18A to F/A-18D

Boeing F/A-18 Hornet 39

A critical element in the HATP plan was the correlation and validation of experimental

and analytical results with results from flight tests of a high-performance aircraft. The

NASA team considered several aircraft configurations for this important task, including

the F-15, F-16, F/A-18, and the X-29 forward-swept wing technology demonstrator aircraft. The advantages and disadvantages of each aircraft for the NASA program were

thoroughly considered, and the F/A-18 was unanimously chosen as the desired test vehicle for several reasons. In flight, the F/A-18 had shown aerodynamic and aeroelastic

phenomena of interest (vortex flows and tail buffet), stall-free engine operation at high

angles of attack, excellent spin recovery characteristics, an advanced digital flight control system, and a large angle-of-attack capability (up to 60-deg trim capability at low

speeds). The Navy’s response to a request from NASA for a preproduction F/A-18 vehicle for the program was very positive. The Navy initially offered NASA an early production F/A-18A aircraft; however, NASA targeted the specially equipped

preproduction F/A-18 (ship no. 6) that had been used at Patuxent River for the spin evaluation phase of the development program. The aircraft had completed its spin tests and

had been stored in a hangar and stripped of its major components as a spare-parts aircraft. However, this particular aircraft was equipped with a special emergency spin

recovery parachute system worth several million dollars and a programmable digital

flight control computer adaptable to the variations desired in the HATP. The Navy

approved the transfer of the stripped aircraft to NASA, and it was trucked to Dryden and

reassembled by experts at Dryden with the Navy’s help into a world-class research aircraft to be known as the F/A-18 High Alpha Research Vehicle (HARV).

F-18 HARV during flow visualization studies using smoke

ejected at apex of LEX and wool tufts on upper surfaces.
F/A-18A to F/A-18D

40 Boeing F/A-18 Hornet

The HATP studies were conducted in three phases. In the first phase, emphasis was

placed on static and dynamic aerodynamic phenomena. This phase included extensive

correlations of wind-tunnel and computational results with data from flight instrumentation on the HARV. These data correlations were conducted with common data sensor

locations on the wind-tunnel models and the HARV. As a result of these aerodynamic

experiments, the capabilities of emerging computational fluid dynamics tools and the

interpretation of wind-tunnel test techniques were aggressively accelerated. Detailed

studies of vortical flow structures emanating from the F/A-18 LEX and interactions with

the vertical tail surfaces resulted in rapid progress in the understanding, prediction, and

minimization of vertical-tail buffet phenomena. Finally, in-depth analysis of the flow

fields shed by the nose and forebody of the F/A-18 resulted in wind-tunnel test procedures and validation of computational codes for future fighters.

An excellent example of the impact of this fundamental research is the LEX uppersurface fences mounted on F/A-18C/D aircraft. These devices greatly alleviate the vertical tail buffeting associated with sudden bursting of the core of the strong vortical flow

shed by the LEX at high angles of attack. McDonnell Douglas developed the fence during parametric wind-tunnel experiments in its own wind tunnel; however, they did not

have the resources or time to identify the flow mechanisms created by the fence. Within

the scope of the HATP, Langley developed a laser vapor screen flow visualization technique that permitted rapid, global assessments of interactive flow fields. Using this

technique, Langley researcher Gary E. Erickson conducted diagnostic tests on an

F/A-18C model in the Navy David Taylor Research Center (DTRC) 7- by 10-Foot Transonic Tunnel, and he precisely identified the vortex-flow mechanisms associated with

the benefits of the fences. The success of the vapor screen system so impressed the Navy

and industry that they requested the Langley vapor screen system on other tests to

understand nonlinear flow behavior at subsonic and transonic speeds.

In the second phase of the HATP, the HARV incorporated a relatively simple and cheap

thrust-vectoring system for studies of aerodynamics at extreme angles of attack, and

engineering development and evaluations of the advantages of thrust vectoring for highangle-of-attack maneuvers. Previous efforts with the Navy involving experiments with

thrust-vectoring vanes on an F-14 inspired the NASA team to adopt this simple concept

instead of a program to develop internal engine vectoring at a cost of many more millions of dollars. (See Langley Contributions to the F-14.) Dryden managed and directed

a contract with McDonnell Douglas to outfit the HARV with deflectable external vanes

mounted behind the engines. The engine exhaust nozzle divergent flaps were removed

and replaced with a set of three vanes for each engine, which resulted in both pitch and

yaw vectoring capability. The specific vane configuration was analyzed and defined by

tests of a powered model in the Langley 16-Foot Transonic Tunnel and the Langley Jet

Exit Test Facility. Meanwhile, the aircraft flight computer was modified to permit

research evaluations within a broad spectrum of thrust-vectoring parameters. The modification of the HARV proved to be extremely challenging, and several members of the

staffs from Langley and Dryden assisted in the final implementation of the hardware and

software of the thrust-vectoring system.

Extensive piloted simulator evaluations of the HARV with thrust vectoring were conducted in the DMS, with results indicating that the implementation of both pitch and

yaw vectoring provided powerful, unprecedented controllability and precision for

maneuvers at high angles of attack.

The results of the F/A-18 HARV thrust-vectoring flights were remarkable. The HARV

became the first high-performance aircraft to conduct multiaxis thrust-vectoring flights,
F/A-18A to F/A-18D

Boeing F/A-18 Hornet 41

and the powerful effectiveness of thrust vectoring at high angles of attack was vividly

demonstrated. The control precision of the aircraft at extreme angles of attack was significantly enhanced, and the vehicle could be stabilized at the conditions for high quality

aerodynamic studies.

In the final phase of the HATP, earlier studies to understand and predict the strong vortex flows emanating from the long pointed fuselage forebody of the F/A-18 were

extended. The studies now included the ability to control these flows for aircraft maneuvers at extreme angles of attack, where yaw control provided by conventional aerodynamic rudders becomes relatively ineffective. Based on in-depth studies conducted by

Langley in several wind tunnels, the HARV was equipped with deflectable foldout

strake surfaces on the forward forebody, and the control system was modified to permit

the pilot to use the strakes for roll control. The strake hardware was engineered and fabricated in Langley machine shops, and the flight computer interface was provided by

Dryden. Results of the flight evaluation of the nose strakes were extremely impressive.

The time required to roll the aircraft through a specific roll attitude change was significantly reduced due to the crisp, powerful control provided by the strakes. At the higher

subsonic speeds, the effectiveness of the strakes approached levels provided by thrust

vectoring in yaw.

The HATP efforts represent a decade of invaluable research and development on key

technologies that will be required for future highly maneuverable high-performance

fighter aircraft, as well as the F/A-18 configuration. The data gathered by NASA has

been widely disseminated among design teams at NASA sponsored national conferences and during site visits. The program has been cited for its high quality, pioneering

value on numerous occasions by industry and DOD. The results of the program are

being used in the development of the next generation F/A-18E/F and other military

aircraft.

Thrust-vectoring vane installation on the F-18 HARV free-flight model with

rectangular box above the vanes representing the container for the spin parachute.
F/A-18A to F/A-18D

42 Boeing F/A-18 Hornet

The Falling-Leaf Maneuver The falling-leaf maneuver originated during World War I as a flight training exercise. In

this exercise, pilots intentionally stalled the aircraft and forced a series of incipient spins

to the right and left. The aircraft descends as it rocks back and forth, much as a leaf does

falling to the ground. In the early 1980’s, an unintentional falling-leaf mode surfaced as

a severe out-of-control problem during developmental flight tests of the F/A-18A. The

out-of-control falling-leaf mode is a highly dynamic mode where the aircraft oscillates

so that it is very difficult to reduce angle of attack and recover. The term “alpha hangup” was used to describe this problem with the F/A-18 and it was a key driver in establishing the aft center of gravity and the maneuvering limits for the aircraft. During early

operational use of the F/A-18, the falling-leaf mode was rarely encountered; however,

by the early 1990’s increasingly aggressive maneuvering had exposed a susceptibility to

the falling-leaf mode with numerous incidents and losses of aircraft.

Langley began studying the falling-leaf mode in 1994 at the request of the Naval Air

Systems Command, following an F/A-18 falling-leaf incident during a routine training

flight that nearly resulted in loss of the aircraft. Under the technical leadership of

Langley researcher John V. Foster, the cause for the falling-leaf mode was identified and

linked to a common aerodynamic stability design method that had been used for many

years. Using the DMS, the critical entry maneuver that excites the mode was identified

and correlated with fleet incidents, and various recovery methods were studied. In addition, the necessary requirements for high-fidelity prediction of the falling-leaf motion in

piloted real-time simulations were defined.

In light of the growing falling-leaf problem on early models of the F/A-18, there was

concern that the emerging F/A-18E/F, which was then preparing for developmental

flight tests, would have the same problem. In response, McDonnell Douglas proposed a

control law design approach, supported by Foster’s research, that specifically targeted

falling-leaf suppression, which was later implemented on the aircraft.

Because no methods existed specifically for falling-leaf flight tests, NASA again used

the DMS facility to develop reliable flight-test techniques that were subsequently validated on the NASA F/A-18 HARV at Dryden. Using these test techniques, falling-leaf

susceptibility was extensively evaluated on the F/A-18E/F during the high-angle-ofattack flight-test program. While the unaugmented aircraft was shown to exhibit the

falling-leaf mode, the new control system design was shown to be very effective in suppressing the mode and the falling-leaf problem was considered solved for that aircraft.

Largely due to the success of the F/A-18E/F program, the Navy is considering retrofitting earlier models of the F/A-18 with the updated control law for the purpose of eliminating the falling-leaf problem.

While the F/A-18 was the most visible recent manifestation of the falling-leaf problem,

numerous other aircraft configurations have exhibited the mode. For example, the

AV-8B exhibited a severe falling-leaf mode that the Foster criteria showed to be a result

of a minor configuration change. As new highly maneuverable configurations are developed and the angle-of-attack envelope expands, Langley’s F/A-18 research has brought

a necessary and timely focus to a critical flight problem.

Flutter Clearance and Tail 

Buffet

In a departure from most fighter programs, flutter clearance tests of both the YF-17 and

the F/A-18A were not conducted in the Langley 16-Foot Transonic Dynamics Tunnel.

Research studies were, however, conducted in the areas of active flutter suppression and

buffet alleviation. A cooperative NASA, Northrop, and Air Force research study was

later conducted to assess the application of active controls for flutter suppression for the
F/A-18A to F/A-18D

Boeing F/A-18 Hornet 43

YF-17 wing-store-pylon combination in the tunnel in late 1977. The results indicated

that active control of wing-store-pylon flutter was possible and that wing leading-edge

surfaces could be effective in such a control system. In 1979 interest in the concept

resulted in an international study of several active flutter suppression systems designed

by British Aerospace and the Royal Aeronautical Establishment from the United

Kingdom, the Office of National d’Etudes et de Recherches Aerospatiales from France,

and Messerschmitt-Bolkow-Blohm from the Federal Republic of (West) Germany. The

TDT tests showed that all the control systems were highly effective in supressing flutter.

The YF-17 testing continued through 1982.

The vertical-tail buffet experienced by the F/A-18A and other high-performance aircraft

resulted in cooperative research by industry, DOD, and NASA on buffet alleviation from

smart materials and actively controlled rudders. Because international allies of the U.S.

use the F/A-18, this research effort included Australia and Canada. The Actively Controlled Response of Buffet Affected Tails (ACROBAT) Program led by Robert W.

Moses investigated the use of an actively controlled rudder, actively controlled piezoelectric devices, and other novel concepts to alleviate vertical-tail buffeting. For the

ACROBAT Program, a 1/6-scale rigid full-span model of the F/A-18 A/B aircraft with

flexible tails was tested in the 16-Foot Transonic Dynamics Tunnel. Numerous control

laws were tested, and many demonstrated buffeting alleviation over a large angle-ofattack range. These tests have been followed up with international ground-based tests of

a buffeting alleviation system on a full-scale F/A-18.

Thrust-Vectoring Research In the early 1970’s, the Navy conducted a vertical and short takeoff and landing

(V/STOL) nozzle study for potential applications to high-performance aircraft. Following this study, the augmented deflector exhaust nozzle (ADEN) was selected as the best

nozzle concept for Navy V/STOL requirements. The ADEN nozzle had a hood, which

deployed from a long upper ramp, that was capable of thrust vector angles from 0 deg to

over 90 deg. Nozzles of this type (long flap on one side of the nozzle and no deploying

hood without VTOL capability) were later called single expansion ramp nozzles

(SERN).

F/A-18 model with 2-D convergent-divergent (CD)

nozzles tested in Langley 16-Foot Transonic Tunnel.
F/A-18E/F

44 Boeing F/A-18 Hornet

In 1975, a joint DOD and NASA two-dimensional (2-D) nozzle workshop held at

Langley formed an ad hoc interagency nonaxisymmetric nozzle working group that

eventually recommended a flight test of 2-D, thrust-vectoring, in-flight thrust-reversing

nozzles. To avoid duplication, studies on potential flight-test vehicles were split up

among NASA (F-15), the Air Force (F-111), and the Navy (YF-17 and F/A-18).

The first full-scale tests, which were sponsored by the Navy, of a 2-D nozzle (ADEN)

were conducted in a Glenn Research Center altitude test cell in 1976. In support of the

Navy studies of advanced nozzles, Langley conducted powered-model tests of an early

F/A-18A configuration with 2-D nozzles in the Langley 16-Foot Transonic Tunnel.

Since the F/A-18A represented the state of the art in fighter design, Langley expanded

the test objectives to include propulsion-airframe integration studies of a number of nozzle types (wedge, 2-D convergent-divergent (CD), SERN), thrust-vectoring concepts,

and in-flight thrust-reversing concepts. The studies also examined F/A-18A vertical-tail

loads, particularly during in-flight thrust-reversing operation. Unfortunately, Navy and

NASA attempts to secure funding for the F/A-18A flight tests were unsuccessful, and

the F/A-18A studies of thrust vectoring were terminated.

F/A-18E/F

The Super Hornet The F/A-18E/F Super Hornet was funded in June 1992 as the replacement for the cancelled Navy A-12 aircraft and as the replacement for the early F/A-18A aircraft and

other Navy and Marine Corps aircraft. The F/A-18E/F is a larger version of the

F/A-18C/D Hornet with extended mission capabilities. The E/F is roughly 25 percent

larger than the C/D, with a 25 percent increase in operating radius and a 22 percent

increase in weapons load capability. First flight of the F/A-18E/F occurred on

November 29, 1995, and preproduction flight tests began in February 1996, at Patuxent

River.

F/A-18E flight test aircraft prepares to land at Patuxent River Naval Air Station.
F/A-18E/F

Boeing F/A-18 Hornet 45

Cruise Performance NASA’s involvement with the F/A-18E/F began in the early stages of the proposed aircraft development when the Office of the Secretary of Defense (OSD) became concerned with the accuracy of McDonnell Douglas’ range estimates for the vehicle. At the

request of OSD, a three-member NASA, DOD, and industry team conducted an independent review of McDonnell Douglas’ F/A-18E/F fighter-escort mission range estimates in April 1992. Langley researcher Gary Erickson represented NASA and called

on supporting analyses from several Langley specialists. Results of the independent

review substantiated the McDonnell Douglas estimates and were briefed to the Assistant

Secretary of Defense. The favorable results from this review were critical to the aircraft

program proceeding to the Defense Acquisition Board for funding advocacy.

Redesign of the Leading-Edge 

Extension

Many operational requirements were revisited as the F/A-18C/D grew to the larger,

heavier F/A-18E/F. Critical performance issues included lift requirements for carrier

approach and wave offs, high-angle-of-attack stability, recovery from extreme attitudes,

and minimization of adverse aerodynamic phenomena such as tail buffet. McDonnell

Douglas explored a number of configuration changes to satisfy these requirements,

including adding a snag to the wing leading edge, reshaping the LEX, and using moveable spoilers on the upper surfaces of the LEX to ensure recovery from extreme angles

of attack.

Low-speed wind-tunnel tests by McDonnell Douglas had indicated that a deflected

spoiler on the upper surface of each LEX would alleviate buffeting of the vertical tails,

promote good lateral-directional stability, and provide trim changes for nose-down control at extreme angles of attack. In May 1992, a series of tests were conducted in the

Langley 8-Foot Transonic Pressure Tunnel to determine the effects of the spoiler concept at higher speeds (Mach numbers from 0.6 to 1.2). Unfortunately, results of the

F/A-18E/F model in 8-Foot Transonic Pressure Tunnel

for evaluations of the LEX spoiler concept.
F/A-18E/F

46 Boeing F/A-18 Hornet

Langley tests indicated that the deployed spoilers would cause an unacceptable decrease

in maximum lift of over 15 percent. With these negative results, a redesign of the LEX

surfaces began. The LEX spoilers have been retained on the F/A-18E/F as speed brakes

and nose-down control devices.

Redesigning the LEX was the job of a 15-member industry, DOD, and NASA team,

which included Langley researchers Daniel G. Murri, Robert M. Hall, and Gary Erickson. This team, which was active for the first 6 months of 1993, initially explored small

modifications to the size and shape of the original F/A-18C LEX to help provide the

required lift and improve lateral-directional stability. However, subsequent wind-tunnel

tests showed that this incremental approach would not be successful and much larger

changes to the LEX configuration would be required. Based on his prior research with

other configurations, Murri proposed more radical LEX candidates that would potentially satisfy these requirements. One of the LEX configurations with favorable windtunnel results that was recommended by Langley was accepted for further refinements

and met all design goals. This configuration was the basis for the final design adopted as

the wing LEX configuration for the production F/A-18E/F.

Extensive tests of the F/A-18E/F with the redesigned LEX were conducted in several

NASA and industry wind tunnels to completely define the aerodynamic characteristics

of the configuration. Data from these tests were used to generate the aerodynamic databases for flight simulation and to develop the flight control software for the aircraft.

NASA engineers worked closely with engineers from McDonnell Douglas and the Navy

to assure that design requirements and national goals were met.

High-Angle-Of-Attack 

Characteristics

Stability and control characteristics of the F/A-18E/F at high-angle-of-attack flight conditions were evaluated in numerous wind-tunnel tests at Langley. In the Full-Scale Tunnel, a combination of static, dynamic, and powered tests was conducted to define and

develop a database for the high-angle-of-attack aerodynamic, stability, and control characteristics of the aircraft. In addition to tests of the basic configuration, tests were

F/A-18E/F (foreground) with redesigned LEX in flight with F/A-18C chase aircraft.
F/A-18E/F

Boeing F/A-18 Hornet 47

conducted to study the impact of fuselage-mounted and wing-mounted stores on aerodynamic and stability characteristics, to assess aerodynamic damping characteristics,

and to assess the magnitude of thrust-induced aerodynamic effects on the configuration.

Free-flight tests were also conducted to provide confirmation of the stability and flight

dynamic characteristics.

This database has been used by McDonnell Douglas and the follow-on Boeing organization, NASA, and the Navy to conduct flight-simulation studies and to aid in the development of the aircraft’s flight control system. An extensive unpiloted and piloted

simulation of the F/A-18E/F has been implemented in the Langley DMS and is being

used to analyze flight control modifications and the impact of aircraft parameters on

high-angle-of-attack behavior.

Spin Tunnel and Drop-Model 

Tests

Hundreds of tests in the Langley Spin Tunnel quantified the spin modes and spin recovery characteristics of the F/A-18E/F, determined the acceptable emergency spin recovery parachute size, and identified the optimal spin recovery procedures prior to flight

tests. Time histories of model motions from these tests were used by McDonnell

Douglas to validate their spin simulation. Data from rotary-balance tests conducted in

this facility provided inputs for an analytical assessment of spin modes, spin recovery

characteristics, and a database for incorporating rotational aerodynamic characteristics

into the flight simulation.

F/A-18E/F drop model immediately after release from the helicopter.
F/A-18E/F

48 Boeing F/A-18 Hornet

A highly sophisticated F/A-18E/F drop model was tested by Langley at the NASA

Wallops Flight Facility to provide risk reduction for the high-angle-of-attack part of the

flight-test program. These tests, which used a 0.22-scale remotely piloted model, supplemented the aircraft flight-test program by providing flight dynamics data for the aircraft at conditions outside the planned operating envelope.

Flutter Tests F/A-18E/F flutter clearance tests were conducted at Langley by Moses G. Farmer in the

16-Foot Transonic Dynamics Tunnel during four tunnel entries from 1993 to 1995.

Phase I tests insured that each pair of dynamically scaled surfaces (wings, horizontal

tails, and vertical tails) was clear of flutter throughout the scaled flight envelope. Phase

II of the tests studied the configuration both with and without stores (bombs and fuel

tanks) mounted on the wings. These tests used the unique two-cable-mount system of

the tunnel, which allows the model to actually fly in the center of the tunnel with assistance from a pilot in the control room. The tests verified that the aircraft was free from

aeroelastic instabilities, including flutter, within its flight envelope. As a result of the

Langley tests, the number of expensive flight tests dedicated to flutter clearance could be

minimized.

In view of Langley’s corporate knowledge of the F/A-18E/F and its predecessors, the

Navy requested NASA involvement when the F/A-18E/F began flight tests. NASA continued to work closely with the Navy and McDonnell Douglas during the engineering

and manufacturing development (EMD) phase. Langley support included flight-test

planning and data evaluation, especially in the high-angle-of-attack regime. In 1997,

Langley assigned an engineer to Patuxent River as a participant in the flight tests and as

a liaison and technical consultant for the test team.

Wing Drop The most recent Langley contribution to the F/A-18E/F Program explored the phenomenon known as wing drop. In March 1996, during flight tests at Patuxent River,

an F/A-18E/F experienced wing drop—an unacceptable, uncommanded abrupt lateral

F/A-18E/F model mounted for flutter tests in the Langley 16-Foot Transonic Dynamics Tunnel.
F/A-18E/F

Boeing F/A-18 Hornet 49

roll-off that randomly occurred and involved rapid bank angle changes of up to 60 deg.

The problem was viewed as extremely serious and posed a threat to operational tests and

the overall development schedule. During the first year of flight tests, the wing-drop

phenomenon was only seen at high altitudes because load restrictions prevented the aircraft from reaching the relevant range of angle of attack at low altitudes. As the loads

test program opened the flight envelope to 7.5g at all altitudes, the full extent of the

wing-drop problem became evident. Objectionable wing-drop events occurred throughout the flight envelope at Mach numbers between 0.5 and 0.9, and this deficiency

became a significant threat to the technical and political health of the F/A-18E/F

Program.

A joint Navy and McDonnell Douglas team concluded that the wing drop was caused by

a sudden, abrupt loss of lift on one of the outer wing panels during maneuvering.

Though the basic cause of the wing drop was determined, how to moderate the airflow

separation differences between the left and right wings was not. A variety of solutions

was explored. For example, 25 potential wing modifications were tested in wind tunnels, computational fluid dynamics studies were undertaken, and two of the potential

fixes were flown with mixed results. In one approach, the use of stall strips in the vicinity of the wing-fold fairing eliminated wing drop, and the aircraft exhibited excellent

flight qualities throughout the envelope. However, the impact of the stall strips on range

and turn performance were severe, and they were discarded as a viable option.

Langley engineer Robert Hall also served on a DOD blue ribbon panel to review the

approach taken by McDonnell Douglas to resolve the wing drop. The panel also participated on various McDonnell Douglas and Navy “tiger teams” that were created to

resolve issues related to the wing-drop problem. Roy V. Harris, a distinguished Langley

retiree, was selected by DOD to head the blue ribbon panel, which subsequently cited

the lack of technical understanding and design tools available in the technical community to address the high subsonic and transonic wing-drop problem. The panel strongly

recommended that a research program be undertaken to develop the design methods

required to avoid this problem in future fighter aircraft. The recommendation was

accepted, and a joint NASA and Navy Abrupt Wing Stall (AWS) Program was initiated.

Langley researchers Jeffrey A. Yetter and Robert Hall served as AWS Program Comanager and Technical Comanager, respectively, with their Navy partners.

As a low impact “80-percent solution” to the F/A-18E/F wing-drop problem, a revised

deflection schedule for the leading-edge flaps was evaluated in flight tests in early 1997,

with very favorable results. Although the leading-edge flap schedule modification significantly reduced the magnitude of the problem, the aircraft still exhibited smaller wing

drops at many test conditions. The original wing-drop problem had been viewed as a

potential safety hazard and a roadblock to productive load tests. After the modification,

the problem was reduced to a flying qualities issue that allowed other tests to continue.

Wind-tunnel tests were conducted at sites other than NASA to evaluate wing changes

that might eliminate the residual wing-drop tendencies. Langley researchers Gary

Erickson and Robert Hall participated in the tests, which continued through the summer

of 1997.

During the winter of 1997 to 1998, the Navy asked NASA for additional assistance in

resolving wing drop. In November 1997, a diagnostic flight test of an F/A-18E/F with

the wing-fold fairing removed was conducted and the results showed that wing drop had

been eliminated from most of the flight envelope. The fairing-off configuration was not

a viable approach for production aircraft, and Langley engineers led by Steven X. S.

Bauer suggested that the flight program apply porosity, a passive technology developed
F/A-18E/F

50 Boeing F/A-18 Hornet

at NASA, to the wing in the fold area. Langley researchers had been conducting experiments with passive porosity to control shock locations and other characteristics for

several years. During the initial concept evaluation on the F/A-18E/F, the porous fairing

was simply a standard wing-fold fairing with areas cut out and a screen mesh substituted. Langley provided design guidelines for the porosity and thickness of the mesh.

This solution, refined by the NASA, Navy, and Boeing team, resolved the wing-drop

problem and permitted continued production of the aircraft.

Additional activities are being conducted to support the joint NASA and Navy AWS

Program, including tests of an F/A-18E/F model in the Langley 16-Foot Transonic Tunnel in September 1999 under the leadership of Robert Hall and S. Naomi McMillin.
Highlights of Research by Langley for the T-45

Boeing T-45 Goshawk 51

Boeing T-45 Goshawk

HIGHLIGHTS OF RESEARCH BY LANGLEY FOR THE T-45

1. At the request of the Navy, Langley participated in an independent assessment team

review of technical progress during early development.

2. Langley conducted exploratory research to define potential wing leading-edge modifications to cure severe low-speed wing drop on the original configuration.

3. Tests were conducted at Langley to determine the spin and spin recovery characteristics of the aircraft and its potential utility as a spin trainer.

4. Langley provided critical tire characterization data that dramatically improved the

modeling and analysis of pilot-induced oscillations during landing.

5. Tests were conducted in the Langley 16-Foot Transonic Tunnel to identify potential

candidates for a revised engine inlet configuration.

SPECIFICATIONS

Manufacturer

Boeing

Date in service

January 1992

Type

Trainer

Crew

Two

Engine

Rolls Royce F405-RR-401

USER

U.S. Navy

DIMENSIONS

Wingspan. . . . . . . . . . . . 30.1 ft

Length . . . . . . . . . . . . . . 39.3 ft

Height . . . . . . . . . . . . . . 14.0 ft

Wing area. . . . . . . . . . .180 sq ft

WEIGHT

Empty . . . . . . . . . . . . . 9,394 lb

Gross . . . . . . . . . . . . . 13,636 lb

PERFORMANCE

Max speed . . . . . Mach number

of 1.04
Highlights of Research by Langley for the T-45

52 Boeing T-45 Goshawk

The Boeing (formerly McDonnell Douglas) T-45 Training System is the first totally

integrated training system developed for and used by the U.S. Navy. It includes the T-45

Goshawk aircraft built by Boeing, advanced flight simulators, computer-assisted

instructional programs, a computerized training integration system, and a contractor

logistics support package. The integration of all five elements produced a superior pilot

in less time and at lower cost than previous training systems. The two-seat, singleengine T-45 Goshawk is the heart of the training system. The T-45 replaces the T-2 and

TA-4 aircraft formerly used for Navy advanced jet trainers. The Goshawk’s design is

based on the British Aerospace Hawk land-based aircraft; however, design modifications have been made to the Goshawk that make the aircraft more suitable for carrierbased operations. The modifications include strengthened landing gear, the addition of

an arresting hook, and catapult launch fittings. The latest version of the aircraft, known

as the T-45C, includes a digital cockpit.

Langley’s involvement in the T-45 began with an independent assessment team review

of technical progress during the initial development program in 1988. Subsequent activities included spin tunnel tests, wind-tunnel research on wing leading-edge modifications, characterization of landing gear tires for improved handling characteristics during

ground rollouts on landing, and wind-tunnel assessments of new engine inlet designs.

Langley facilities involved in support of the T-45 Program included the 16-Foot Transonic Tunnel, the 12-Foot Low-Speed Tunnel, the 20-Foot Vertical Spin Tunnel, and the

Landing Loads Facility.
Langley Contributions to the T-45

Boeing T-45 Goshawk 53

LANGLEY CONTRIBUTIONS TO THE T-45

Early Configuration 

Development

The U.S. Navy initiated the Advanced Trainer (VTX) Program in the early 1980’s to

replace the existing T-2 Buckeye and TA-4 Skyhawk advanced jet trainers. Industry

responses to the Navy request for proposals (RFP) included several existing and new

aircraft configurations. A team from McDonnell Douglas and British Aerospace proposed both a modification of the existing British Hawk land-based configuration and a

new trainer. The VTX contract was awarded to the McDonnell Douglas and British

Aerospace team in November 1981. The Boeing (formerly McDonnell Douglas) T-45

Goshawk evolved from the Hawk design.

Conversion of the Hawk land-based aircraft to a naval trainer with carrier capabilities

involved considerable research and development. In addition to the necessary strengthening of landing gear components and the inclusion of arresting gear, development work

was required in numerous areas that were critical for carrier-based operations. Some

areas of concern included the handling qualities, engine response characteristics, and

stall characteristics of the T-45.

In 1988, following extensive preliminary flight-test evaluations by the Navy at the

Patuxent River Naval Air Station in Maryland, the Navy cited several major deficiencies

in the T-45. The deficiencies included high approach speed, slow engine thrust response,

and longitudinal and lateral stability deficiencies. McDonnell Douglas and British

Aerospace developed candidate solutions and recommended approaches to resolve these

issues. In 1989 the Navy convened a blue ribbon independent assessment team to review

the technical status and plans for the program. In response to a request from the Navy

for Langley representation, Joseph R. Chambers served on the team.

Stall Characteristics The stall characteristics of the initial T-45 configuration were judged to be unacceptable

by the Navy on the basis of a severe wing-drop behavior at the stall and high approach

speeds (aggravated by the increased weight required to strengthen the airframe for

Langley researchers Long P. Yip and Holly M. Ross examine a T-45 model with a

discontinuous leading-edge modification in the Langley 12-Foot Low-Speed Tunnel in 1989.
Langley Contributions to the T-45

54 Boeing T-45 Goshawk

carrier operations). During the Navy’s flight evaluations, the wing drop was so severe

that uncommanded roll motions often exceeded 90 deg.

While McDonnell Douglas and British Aerospace explored various candidate solutions

to the wing-drop issue, Langley proposed a joint research project to assess the effectiveness of a Langley concept for enhanced stall characteristics. As part of research to

improve stall and spin characteristics of general aviation aircraft, Langley had conceived a wing leading-edge modification that significantly improved the lateral stability

and spin resistance of several general aviation research aircraft during stall-spin

research flight tests. The leading-edge modification consisted of a discontinuous “snag”

at about the 75-percent span location that acted similar to an aerodynamic fence and

maintained attached flow on the outer wing panel to very high angles of attack (beyond

stall). Although the wing leading-edge radius of the T-45 was much smaller than those

of general aviation aircraft, it was hoped that the modification would also be effective

for the advanced trainer.

Led by Langley’s Long P. Yip, tests were conducted on a 0.15-scale T-45 model in the

Langley 12-Foot Low-Speed Tunnel. The test techniques included conventional static

force tests as well as single-degree-of-freedom free-to-roll tests to determine wing-drop

tendencies. The results of the investigation indicated that the wing modification was

effective in minimizing wing-drop tendencies for the cruise configuration; however, the

modification was not effective for the landing configuration with the wing trailing-edge

flaps deflected. The T-45 Program subsequently adopted a wing redesign, which incorporated wing leading-edge slats. The slats virtually eliminated the wing-drop tendency

and lowered the carrier-approach speed to a more acceptable value.

Spin Characteristics Flight-test experience with the British Hawk aircraft had indicated that the aircraft was

very reluctant to spin and that attempts to intentionally spin the aircraft usually resulted

T-45 model undergoing test in the Langley Spin Tunnel.
Langley Contributions to the T-45

Boeing T-45 Goshawk 55

in a spiral with rapidly increasing airspeed. The Hawk recovers from the high-speed spiral when controls are neutralized. Spin tests of the T-45 in the Langley 20-Foot Vertical

Spin Tunnel by Langley researcher Raymond D. Whipple indicated that the Goshawk

would exhibit similar characteristics. In fact, it was virtually impossible to obtain spins

for the T-45 model in the normal upright attitude because, after being hand launched

with prerotation into the vertical airstream, the model would immediately nose over and

rapidly increase airspeed beyond the test capability of the Spin Tunnel.

Full-scale flight tests of the T-45 subsequently verified the predictions of the Langley

Spin Tunnel tests. During spin attempts, airspeed rapidly increased, and stabilized spins

could not be obtained. As a result of this spin resistant behavior, the T-45 is not used for

spin training. (The T-2 and TA-4 had been used for spin training.)

Ground Handling In 1999, the Navy requested that Langley provide data, analysis, and recommendations

to eliminate a severe pilot-induced oscillation (PIO) resulting in erratic yaw behavior of

the T-45 during runway rollout in land-based landing operations. The Navy also

requested assistance in determining the cause of uncontrollable aircraft yaw when tires

failed.

In response to the Navy requests, Langley researcher Robert H. Daugherty led a

Langley effort that conducted over 160 aircraft main and nose tire tests to define cornering and braking behavior in the T-45. The Langley team conducted on-site tests at

Patuxent River with a special truck apparatus in a program that included evaluations of

various tire states, including normal and blown tires. The tests determined the effect of

aircraft roll attitude on uncommanded tire cornering force, identified the drag behavior

of failed main gear tires and the reason for lack of yaw control, and provided models of

The T-45 tire characteristics during landing rollout were studied by Langley.
Langley Contributions to the T-45

56 Boeing T-45 Goshawk

physical tire behavior for analysis. A particularly valuable output of this effort was a

dramatic improvement in the modeling capability of T-45 landing operations and the

inclusion of the data generated by Langley in the T-45 rollout and training simulators.

After the Langley data had been incorporated in the simulator, the landing dynamics of

the simulated aircraft were significantly more realistic. The T-45 Program was especially complementary in recognizing this effort as a timely, critical, and valuable NASA

contribution to the program.

Inlet Performance Flight-test experience with the T-45 has demonstrated that the aircraft sometimes experiences undesirable propulsion system characteristics during certain maneuvers. In particular, the aircraft engine has experienced self-clearing “pop” stalls, pop surges, and

occasional locked-in surges during simulated air-combat maneuvers and recovery

maneuvers from aircraft (wing) stalls.

As a result of concern over these characteristics, the Navy requested that Langley provide support to, and participate in, wind-tunnel tests of the engine inlet behavior of the

T-45. In support of this request, a Langley, Navy, and Boeing Team conducted two separate T-45 test entries (May 1998 and July 1999) in the Langley 16-Foot Transonic Tunnel. Langley researcher E. Ann Bare led the test operations.

The 0.26-scale inlet distortion model used in the tests consisted of the T-45 forebody,

fuselage contour to the wing trailing edge, and wings. The model was powered with an

aft-mounted ejector and included extensive instrumentation to measure steady state and

dynamic pressure distortion characteristics. The scope of the test program included evaluations of minor and moderate inlet changes for the cruise and power approach configurations of the T-45.

T-45 inlet performance model in the Langley 16-Foot Transonic Tunnel.
Highlights of Research by Langley for the A-10

Fairchild Republic A-10 Thunderbolt II 57

Fairchild Republic A-10 

Thunderbolt II

HIGHLIGHTS OF RESEARCH BY LANGLEY FOR THE A-10

1. At the request of industry and the Department of Defense, Langley personnel participated in reviews and assessments during competitive stages of Attack Experimental

(A-X) Program.

2. Langley conducted wind-tunnel tests and provided data for all competing designs in

A-X Program.

3. Langley and Fairchild conducted joint tests of a powered A-10 model in the 7- by

10-Foot High-Speed Tunnel to determine the effects of engine exhaust on aerodynamic characteristics.

4. Fairchild consulted with Langley personnel on A-10 wing airfoils, stall characteristics, high-lift aerodynamics for low-level maneuvers, and spin characteristics.

5. Langley conducted extensive spin tunnel tests of the A-10 for a variety of external

store configurations.

SPECIFICATIONS

Manufacturer

Fairchild Republic

Date in service

March 1976

Type

Close support and attack

Crew

One

Engine

General Electric TF34-GE100A

USER

U.S. Air Force

DIMENSIONS

Wingspan. . . . . . . . . . . . 57.5 ft

Length . . . . . . . . . . . . . . 53.3 ft

Height . . . . . . . . . . . . . . 14.7 ft

Wing area. . . . . . . . . . .506 sq ft

WEIGHT

Empty . . . . . . . . . . 18,591.0 lb

Typical combat . . . 23,498.0 lb

PERFORMANCE

Max speed . . . . . Mach number

of 0.56

Radius of action. . . . . 695 n mi
Highlights of Research by Langley for the A-10

58 Fairchild Republic A-10 Thunderbolt II

The Fairchild Republic A-10 was the result of the Air Force’s A-X competition that

began in 1967 for a close-support aircraft capable of withstanding the highly lethal environment near the front lines. During the A-X competition, the Department of Defense

(DOD) requested that Langley participate in mission analyses, conduct supporting

wind-tunnel tests, and provide analyses of the competing designs. During the summer of

1967, tests were conducted in the Langley 7- by 10-Foot High-Speed Tunnel on designs

submitted by Grumman, Northrop, McDonnell, and General Dynamics. In 1970, the

requirements for the A-X mission were changed, and the Air Force issued a new request

for proposals (RFP). Six companies responded to the RFP, and designs by Fairchild and

Northrop were selected for further development. In preparation for a competitive fly off

under the “fly before buy” philosophy, Langley conducted performance and spin tunnel

tests of the Fairchild Republic and Northrop configurations, known as the YA-10A and

the YA-9A, respectively.

After the Air Force selected the A-10 as its close-support aircraft in January 1973,

Langley conducted extensive tests in the Langley 20-Foot Vertical Spin Tunnel of the

production configuration with a large variety of external stores. Langley facilities used

in support of the A-10 Program also included the 7- by 10-Foot High-Speed Tunnel.
Langley Contributions to the A-10

Fairchild Republic A-10 Thunderbolt II 59

LANGLEY CONTRIBUTIONS TO THE A-10

The A-X Competition In the Vietnam conflict concentrated small-arms fire, ground-to-air missiles, and other

more sophisticated defenses were particularly lethal to aircraft flying close-support missions. This situation resulted in dramatic changes in philosophy for the capabilities of

aircraft conducting these missions. Specialists at Langley were asked to identify technologies that could be applied to a hard-maneuvering aircraft with a relatively high

degree of survivability. In March 1967, the Air Force released a request for proposals

(RFP) for a new Attack Experimental (A-X) Program. In 1967, numerous wind-tunnel

tests were conducted in the Langley 7- by 10-Foot High-Speed Tunnel to obtain analysis

data for designs by Grumman, Northrop, McDonnell, and General Dynamics. The tests

were led by William P. Henderson and Linwood W. McKinney, who conducted extensive briefings for the Department of Defense (DOD) and the industry competitors on the

merits of each configuration.

In the years following 1967, the A-X mission requirements began to change as the threat

of Soviet armor and all-weather operations became embedded in military priorities. In

1970, a new A-X RFP was released by the Air Force and six companies responded.

After a formal study, Northrop and Fairchild were named as final competitors for a fly

off competition at Edwards Air Force Base.

In 1971, tests of a powered model of the Fairchild A-10 were conducted in the 7- by

10-Foot High-Speed Tunnel by Vernon E. Lockwood. The principal objective of the

tests was to determine the effects of engine exhaust flow on aerodynamic characteristics

in high-power conditions. The tests were conducted with a special model installation in

which the powered engine nacelles were not mounted directly to the airframe, but to a

separate sting that included air supply lines for the simulation of power. Critical data

were obtained on the impact of power on performance and stability of the configuration,

including ground effects.

Powered-model tests of the Fairchild A-10 with engines supported by an

auxiliary upper sting in the Langley 7- by 10-Foot High-Speed Tunnel.
Langley Contributions to the A-10

60 Fairchild Republic A-10 Thunderbolt II

Spin Recovery In 1972, tests were conducted in the Spin Tunnel by Stanley H. Scher for the competing

Northrop (A-9) and Fairchild (A-10) A-X configurations. Results of these tests were

used for evaluations and planning for the competitive fly off that occurred at Edwards

Air Force Base later that year. In addition to providing information on advantages and

disadvantages of each configuration, these results provided spin and recovery characteristics for pilots of the respective vehicles.

The Fairchild aircraft was announced as the winner of the competition on January 18,

1973, and a formal request for tests in the Langley Spin Tunnel for the development program was received from the Air Force. A large number of tests were conducted because

of the variety of external stores, tanks, and armament carried by the aircraft.

High Reynolds number tests were performed with an A-10 model at spin attitudes in the

NASA Ames Research Center 12-Foot Pressure Tunnel prior to the spin tunnel tests to

determine whether the model would exhibit significant scale effects, and if so, what

modifications might be made to correct for these effects. Results of the tests at Ames

showed no appreciable scale effects for angles of attack below about 75 deg, but appreciable scale effects (more prospin yawing moments at low Reynolds numbers) for

angles of attack above 75 deg. Nose strakes were sized to artificially compensate for the

scale effects, but no flat spins (angle of attack greater than 75 deg) were evident and the

strakes were not used.

Spin tunnel tests of the A-10 configuration.
Highlights of Research by Langley for the F-111

General Dynamics F-111 Aardvark 61

General Dynamics F-111 Aardvark

HIGHLIGHTS OF RESEARCH BY LANGLEY FOR THE F-111

1. Langley conducted studies to enable the variable-sweep wing that was employed by

the F-111 and subsequent variable-sweep aircraft such as the F-14 and B-1.

2. Langley staff conducted wind-tunnel tests, identified major problems, and recommended critical improvements to the aerodynamic performance of the F-111.

3. Langley personnel presented key technical results in congressional and high level

Department of Defense investigations of the technical merit of the F-111.

4. Langley led studies to provide solutions to major propulsion integration problems

exhibited by the F-111, which were used on all subsequent high-performance fighters, such as the F-14, F-15, and F-22.

5. Langley identified critical deficiencies in the high-angle-of-attack characteristics of

the F-111.

6. Langley detected the presence of a dangerous flat spin for the F-111 and precipitated the development of a stall inhibitor system to protect against inadvertent

spins.

7. Following a catastrophic wing fatigue failure of an operational F-111, Langley conducted critical materials tests, and Langley personnel served on advisory boards to

recommend approaches to ensure safety of the fleet.

8. Langley conducted tests to improve the robustness and landing loads of the F-111

crew module.

9. Langley wind-tunnel tests to determine the flutter characteristics of the F-111 identified a potential tail flutter problem that resulted in modifications to the aircraft.

10. Langley supercritical wing technology was applied to the F-111 and demonstrated

during the TACT and MAW Programs.

SPECIFICATIONS

Manufacturer

General Dynamics

Date in service

June 1967

Type

Fighter-bomber

Crew

Two

Engine

F-111F . . . Pratt & Whitney 

TF30-P-100

USERS

U.S. Air Force (retired 1996) 

and Australian Air Force

DIMENSIONS

Wingspan

unswept. . . . . . . . . . . 63.0 ft

fully swept . . . . . . . . 31.9 ft

Length . . . . . . . . . . . . . . 73.5 ft

Height . . . . . . . . . . . . . . 17.1 ft

Wing area. . . . . . . . . . .525 sq ft

WEIGHT

Empty . . . . . . . . . . . . 47,481 lb

Gross . . . . . . . . . . . . 100,000 lb

PERFORMANCE

Max speed . . . . . . . above Mach

number of 2

Range. . . . . . . . . . . . 2,925 n mi
Highlights of Research by Langley for the F-111

62 General Dynamics F-111 Aardvark

The General Dynamics F-111 was a multipurpose supersonic tactical fighter-bomber

aircraft. The F-111 was one of the more controversial aircraft in the U.S. military inventory, yet it achieved one of the safest operational records in Air Force history. It was

regarded as a highly effective, all-weather interdiction aircraft. As the result of a high

level government directive in 1961, both the Navy and Air Force became committed to a

common Tactical Fighter Experimental (TFX) Program. The TFX Program called for

developing a single aircraft to fulfill a Navy fleet defense interceptor requirement and an

Air Force supersonic strike aircraft requirement. The mission requirements were impossible to achieve, especially since planners placed priority upon the Air Force requirement, and then tried to tailor a heavy land-based aircraft to the demands of carrier-based

naval aircraft. The naval version, the F-111B, was never placed into production. The Air

Force aircraft was produced in a variety of models, including the F-111A, F-111D,

F-111E, and F-111F fighter-bombers; the FB-111A strategic bomber; the F-111C for

the Australian Air Force; and an EF-111 electronic warfare version. The U.S. Air Force

versions were retired in 1996, but the Australians plan to operate their fleet until well

into the twenty-first century.

Arguably, the political and technical issues associated with the F-111 program resulted

in more research activities at the Langley Research Center than any other production

military aircraft in Langley’s history. The staff participated in top level assessments of

the aircraft’s capabilities (including briefings at the highest levels of the Department of

Defense (DOD) and government), identified several critical problems, and provided recommendations for solutions. Significant Langley technical contributions included the

variable-sweep wing concept, and test activities in aerodynamic performance enhancements, high-angle-of-attack characteristics, spin recovery, flutter, propulsion integration, wing structures and materials, and robustness of the crew escape module. Finally,

Langley was a major participant in the joint NASA and Air Force F-111 Transonic Aircraft Technology (TACT) Program and the Mission Adaptive Wing (MAW) Program

that applied supercritical wing technology, which was developed at Langley, through

flight tests of a modified F-111 research aircraft at NASA Dryden Research Center.

Langley facilities that contributed to the F-111 program included the 7- by 10-Foot

High-Speed Tunnel, the 4- by 4-Foot Supersonic Pressure Tunnel, the Unitary Plan

Wind Tunnel, the 16-Foot Transonic Tunnel, the 8-Foot Transonic Pressure Tunnel, the

26-Inch Transonic Blowdown Tunnel, the 30- by 60-Foot (Full-Scale) Tunnel, the

20-Foot Vertical Spin Tunnel, the 16-Foot Transonic Dynamics Tunnel, the Fatigue and

Fracture Laboratory, the Impact Dynamics Research Facility, the 12-Foot Low-Speed

Tunnel, and radio-controlled drop models.
Langley Contributions to the F-111

General Dynamics F-111 Aardvark 63

LANGLEY CONTRIBUTIONS TO THE F-111

The Variable-Sweep Wing 

Concept

The F-111 was the first production military aircraft to capitalize on years of Langley

research to develop a variable-sweep wing aircraft. Variable-sweep wings provide significant benefits to the aerodynamic performance of aircraft that operate over a wide

range of altitudes and airspeeds. An excellent summary of the history of Langley’s role

in the development of this breakthrough concept was given by Edward C. Polhamus

(contributor to variable-sweep research and the F-111 program) in his 1983 American

Institute of Aeronautics and Astronautics (AIAA) Wright Brothers Lecture (ref. 4).

As the advantages of wing sweep for enhanced aerodynamic performance became

known near the end of World War II, designers considered several approaches to providing variable sweep for efficient characteristics at both low and high speeds. The German

Messerschmitt P-1101 research configuration had provisions for three groundadjustable sweep angles; however, the aircraft was only carried to the prototype stage

and flight tests were never conducted. Although it never flew, the P-1101 was captured

and brought to the United States, where it was later evaluated by Bell Aircraft Corporation in a study that strongly influenced the design of the Bell X-5 research aircraft.

The first wind-tunnel tests of variable-sweep concepts were conducted at Langley in the

mid-1940’s. These tests included the now familiar symmetric variable-sweep wing, as

well as the variable oblique-wing concept (free-flight model tests by John P. Campbell).

Researcher Charles J. Donlan, who would later become Deputy Director of Langley, initiated tests of an existing model of the famous Bell X-1 (first aircraft to exceed the

sound barrier) in the Langley 300-MPH 7- by 10-Foot Tunnel in 1947 to explore the

challenges of variable sweep. The results of the study, which used a single centerline

pivot for the wing, clearly showed that such an arrangement resulted in excessive longitudinal stability and marginal maneuverability with the wings swept aft. To be successful, the variable-sweep concept would have to minimize the dramatic increase in

stability. Several methods were explored, and it was concluded that some type of variable longitudinal translation of the pivot point was required—although this solution was

undesirable from a weight and complexity perspective.

Time-lapse photograph of the Bell X-5 shows the wing at various sweep angles.
Langley Contributions to the F-111

64 General Dynamics F-111 Aardvark

In the late 1940’s, under somewhat reluctant Air Force sponsorship and based on the

German and U.S. studies, the Bell X-5 became the Air Force and the National Advisory

Committee for Aeronautics (NACA) workhorse for variable-sweep studies. Wing sweep

on the X-5 could be continuously varied from 20 deg to 60 deg through the use of a

translating wing-pivot mechanism. The X-5 configuration was tested in the Langley

300-MPH 7- by 10-Foot Tunnel, the 8-Foot Transonic Pressure Tunnel, the 4- by 4-Foot

Supersonic Pressure Tunnel, and the 20-Foot Vertical Spin Tunnel. The first flight of the

X-5 was made on June 20, 1951. At about the same time, interest in variable sweep was

growing in the United Kingdom, and discussions between Langley Assistant Director

John Stack and the British resulted in exchanges of data and proposed cooperation for

research efforts.

In 1952, the Grumman XF-10F variable-sweep aircraft began flight tests. (The XF-10F

had also been tested in the 7- by 10-Foot High-Speed Tunnel at Langley.) Although the

aircraft was underpowered and subsonic, it demonstrated the aerodynamic performance

advantages of variable sweep. However, the wing-pivot translation feature added considerable weight to the configuration, and the performance of the XF-10F could not

compete with the rapid increase in supersonic performance that was being demonstrated

on most military aircraft of its size.

At this point, military interest in the variable-sweep concept rapidly decreased. It

appeared that supersonic flight could not be sustained with state of the art engines at that

time. Also the heavy, complicated translating wing-pivot mechanism was not an acceptable penalty when compared with the performance of a moderately swept fixed wing.

However, as has been the case throughout Langley’s history, a few visionaries correctly

anticipated the future military aircraft requirements for sustained supersonic flight and

successfully advocated for fundamental research to continue to develop and optimize

The radical British Swallow configuration in the Langley 16-Foot Transonic Tunnel

with variable sweep arrow wing and over and under wing-mounted engines.
Langley Contributions to the F-111

General Dynamics F-111 Aardvark 65

the variable-sweep concept. Led by John Stack and Charles Donlan, Langley researchers joined with the British in a North Atlantic Treaty Organization (NATO) sponsored

cooperative study of variable-sweep concepts that included extensive tests in the

Langley 7- by 10-Foot High-Speed Tunnel and the 16-Foot Transonic Tunnel.

The British and Langley cooperative tests in 1958 included work on the British Swallow

configuration, which was a radical tailless slender arrow-wing configuration with variable-sweep wings and pivoting wing-mounted engines. The Swallow exhibited numerous stability and control problems. Langley brought three variable-sweep configurations

to the study, including two that used pivot locations in the fuselage near the trailing edge

of the inner wing and folding tail control surfaces to maintain stability levels.

Thomas A. Toll, responsible for the stability portion of the variable-sweep program,

assigned William J. Alford, Jr. and Edward Polhamus to the task. In 1959 they arrived at

the breakthrough solution, which was to locate the pivots of the movable wing panels to

positions outboard of the fuselage. With this outboard wing-pivot arrangement, sharing

of lift between the fixed inner wing and the movable outer wing panels minimized the

movement of the aerodynamic center of lift. A fourth configuration, known as configuration IV, was added to the research program to confirm this design concept. The configuration was tested across the speed range in Langley tunnels with great success.

Encouraged by their success, the Langley team conducted in-depth analyses of variablesweep aircraft representative of configurations for Navy and Air Force missions. Tests

of all types—force and moment, dynamic, and free flight—were conducted in virtually

all of the major tunnels at Langley. Variable-sweep configurations applicable to the

Navy combat air patrol mission were studied in a program known as CAP, and the Air

Force tactical aircraft mission was the basis for configurations studied in a program

known as TAC. Extensive wind-tunnel tests and analysis by Langley researchers had

matured the variable-sweep concept.

Alford and Polhamus became internationally recognized for their research on the outboard wing-pivot concept, and they mutually hold the U.S. patent on this revolutionary

discovery, which has been successfully applied to numerous U.S. and foreign military

aircraft.

Configuration IV, which was the breakthrough

model for variable-sweep technology.

James L. Hassell, Jr. with a free-flight CAP model that

was flown in the Langley Full-Scale Tunnel.
Langley Contributions to the F-111

66 General Dynamics F-111 Aardvark

The Tactical Fighter 

Experimental (TFX) Program

In 1957, the U.S. Navy requested industry responses for the design of a low-altitude

strike fighter. John Stack briefed senior Navy managers that a proposed British lowaltitude strike fighter, the NA-39, would be much more advanced than the Navy aircraft.

He also suggested the application of variable sweep to leapfrog the capabilities of the

NA-39. Following briefings by Langley personnel to the Navy, the mission specifications for the new Navy fighter were expanded to include multimission capability with a

requirement that variable-sweep applications be studied. The request for proposals went

to industry in early December 1959 and set the stage for what would ultimately become

the Tactical Fighter Experimental (TFX) Program.

Meanwhile, the Air Force Tactical Air Command (TAC) Requirements Division at

Langley Air Force Base (adjacent to the Langley Research Center) was attempting to

define a replacement for the F-105 fighter-bomber aircraft. TAC was interested in an aircraft that could carry nuclear weapons internally, fly transatlantic routes without refueling, operate from semiprepared fields in Europe, have a top speed of Mach number of

2.5 at high altitudes, and fly at high subsonic speeds at low altitudes. The aircraft would

perform a “low-low-high” mission, wherein it would cruise into the vicinity of the target

at low altitudes and subsonic speeds, perform a low-altitude dash to the target at high

subsonic speeds, and perform a high-altitude, long-range cruise back to base at subsonic

speeds. The Mach number of 2.5 capability would be used for high-altitude engagements against enemy fighters. Initial analysis by industry of the request indicated that a

fixed-sweep aircraft capable of meeting the requirements would weigh in excess of

100,000 lb (too heavy for unprepared fields) and demand the attributes of low sweep for

transatlantic flight, but high sweep for the high-speed requirements. TAC was therefore

in a stalemate without a viable design approach to its requirements.

John Stack approached the TAC planners in 1959 with the benefits of variable sweep to

enable an aircraft to meet the requirements. The extended ferry range that is provided by

variable sweep was of prime importance to TAC, since estimates indicated that transatlantic range might be possible. Together with the commander of TAC, Stack laid out a

realistic set of aircraft performance requirements that included the desired low-altitude

dash capability at high subsonic speeds. Unfortunately, as the requirements went

through the TAC system for approval, the final specifications called for a 210-n-mi, sea

level dash at a speed that had increased from a Mach number of 0.9 to a Mach number

of 1.2. Upon learning of the supersonic low-altitude speed requirement, Langley quickly

informed the Air Force that this capability was impossible to meet for the range specified. Nonetheless, TAC was committed to the unrealistic specification. (In flight tests of

the F-111A in 1969, the actual low-altitude supersonic dash performance of the aircraft

was only 30 n mi.)

In 1960, the Air Force and the Navy were both attempting to develop new fighter aircraft. The Kennedy administration’s Secretary of Defense, Robert McNamara, ordered

the development of a single aircraft for both the Air Force and the Navy (to be led by the

Air Force), called the Tactical Fighter Experimental (TFX). Mr. McNamara defined the

basic mission requirements when the Air Force and Navy could not agree, and in October 1961, a request for proposals (RFP) was issued to industry. Boeing won all four

stages of the competition that followed, but McNamara overruled the source selection

board and decreed on November 24, 1962, that the General Dynamics and Grumman

Team would build the TFX.

Langley’s variable-sweep wing concept was nationally recognized as the technical key

that would unlock the capabilities of the TFX. McNamara said (ref. 27)
Langley Contributions to the F-111

General Dynamics F-111 Aardvark 67

New developments in engine performance and in aerodynamics, particularly the variable-geometry wing concept evolved by NASA, now

make it possible to develop a tactical fighter that can operate from

aircraft carriers as well as from much shorter and cruder runways,

and yet can carry the heavy conventional ordnance loads needed in

limited war.

As an example of the plaudits given Langley for the variable-sweep contribution to the

evolving TFX program, the following comments of editor Robert Hotz of the internationally acclaimed Aviation Week magazine appeared in the magazine on December 3,

1962:

Underlying the whole TFX concept is one of the solid, basic technical

explorations of the old National Advisory Committee for Aeronautics

(NACA) that did so much to keep this country the international leader

in supersonic aircraft development. Without the fundamental research

into the variable-sweep wing and the detailed development of this

principle by the Langley research laboratory group headed by John

Stack, the current TFX concepts of both final competitors would have

been impossible... When Congress convenes again and begins carping

over the Fiscal 1964 NASA budget for aeronautical research, the full

story of the Langley contributions to the TFX program should be hammered home as an example of how these research and development

investments eventually pay substantial benefits.

After the TFX contract was awarded, Langley, Ames, Glenn, and Dryden all supported

the F-111 development program. Because of the strong interest in this aircraft, and the

large magnitude of NASA support, the program was rigorously managed and documented, beginning in November 1962. Mark R. Nichols, Laurence K. Loftin, Jr.,

Edward Polhamus, Jack F. Runckel, Theodore G. Ayers, and M. Leroy Spearman were

the leaders and spokesmen for the F-111 support activities at Langley. In addition,

Polhamus served as the Langley focal point for overall F-111 activities and spent considerable personal time in coordination of tunnel requests and NASA, industry, and

DOD joint meetings.

In 1963, political turmoil surfaced as a special Senate subcommittee chaired by Senator

McClellan of Arkansas held hearings on the award of the TFX Program. This committee

gathered a considerable amount of Langley data, briefings, and testimony during various

phases of the hearings, which took place over several years.

For the first 3 years of the F-111 development program (1963 to 1965), a total of nearly

20,000 hr of tests were conducted in NASA wind tunnels (about 15,000 hr at Langley).

Over 15 wind tunnels were utilized, making the F-111 program the most extensive

wind-tunnel support effort ever provided for one aircraft by NASA or the NACA. By

1968, over 22,000 hr of tunnel tests had taken place at Langley. (In contrast, Langley

expended 5,000 hr for development of the F-105.) The large number of test hours was

the result of the multiple versions of the aircraft (F-111A, F-111B, RF-111, and

FB-111), the addition of wing sweep as a test variable, a vast number of external store

configurations, and concentrated technical assaults on a multitude of problems—

especially the transonic drag issue. During the development effort, the Langley staff also

participated in numerous F-111 advisory and assessment teams and briefings for DOD,

Congress, and industry. For example, Edward Polhamus presented the scope and results

of the NASA effort to the McClellan Committee during its second session in 1970.
Langley Contributions to the F-111

68 General Dynamics F-111 Aardvark

The first F-111A flew in December 1964, and the first F-111B flew in May 1965. The

most positive result from early flight evaluations was the very satisfactory behavior of

the variable-sweep wing system. However, the aircraft were judged to be sluggish and

underpowered. Furthermore, the engines exhibited violent stalling and surging characteristics.

An outstanding, in-depth discussion of the details of the initiation and early years of the

F-111 development program is given in the book Illusions of Choice by Robert F.

Coulam and Robert S. McNamara (ref. 27).

Aerodynamic Performance On December 19, 1962, representatives of General Dynamics and Grumman visited

Langley for discussions of the supersonic performance of the F-111. The manufacturers

were informed that the supersonic trim drag of the aircraft could be significantly

reduced and maneuverability increased by selecting a more favorable outboard wingpivot location. Unfortunately, the manufacturers did not act on this recommendation,

and it was subsequently widely recognized that the F-111 wing pivots were too far

inboard. (It should be noted that the F-14 designers, aware of this shortcoming, designed

the F-14 with a more outboard pivot location.) The F-111 subsequently exhibited very

high levels of trim drag at supersonic speeds during its operational lifetime.

In March 1963, the initial supersonic tests of the F-111 in the Langley Unitary Plan

Wind Tunnel by David S. Shaw confirmed the Langley expectations of high trim drag at

supersonic speeds. A month later, tests conducted by Theodore Ayers of a 1/24-scale

F-111 model at transonic speeds in the Langley 8-Foot Transonic Pressure Tunnel indicated that the transonic drag was considerably higher than General Dynamics predictions. Therefore, a large drag reduction had to be accomplished to meet mission

requirements. Several discussions between Langley and General Dynamics were also

held to define approaches to improve supersonic maneuverability. Langley continued to

emphasize the importance of wing-pivot location and recommended a change in pivot

location and a forward shift of the wing as a solution to the problem. It was decided that

the modified wing suggested by Langley would be built and tested. Supersonic tests of

the Langley wing modification indicated a large increase in maneuverability that would

allow the F-111 to approach the proposed maneuverability levels. However, because of

changes in maximum cross-sectional area, some transonic drag penalty would be

Supersonic tests of the early F-111 design in the

Langley Unitary Plan Wind Tunnel in 1963.
Langley Contributions to the F-111

General Dynamics F-111 Aardvark 69

expected with the modification. At a later meeting in June between Langley, the F-111

Systems Program Office (SPO), and General Dynamics, the positive results of the modified wing were discussed, but the F-111 SPO expressed concerns over any possible

transonic drag penalty, the engineering effort required for the change, and potential

schedule slippage. The Air Force cancelled further studies of the wing modification.

Meanwhile, a controversy erupted over the discrepancy of transonic drag estimates

between the data obtained by Theodore Ayers in the Langley 8-Foot Transonic Pressure

Tunnel and data obtained in the Cornell Aeronautical Laboratory 8-Foot Transonic Pressure Tunnel. The Langley staff investigated these differences and concluded that the

lower drag measured in the Cornell facility was probably due to interference effects

caused by an oversized model and the large, blunt support sting. Langley offered to

investigate the problem by testing a mock-up of the Cornell support system. In October

1963, special tests were conducted in the Langley 8-Foot Transonic Pressure Tunnel

with a mock-up of the Cornell support system. The results of the test indicated a very

large buoyancy effect, which accounted for the erroneous low transonic drag measurements in the Cornell tunnel. As Langley’s support for the F-111 continued, the staffs of

the 16-Foot Transonic Tunnel and the 8-Foot Transonic Pressure Tunnel remained sensitive to wind-tunnel accuracies, and numerous tests were conducted with the same model

in these two tunnels to establish confidence in the Langley projections of transonic drag.

With a much higher level of drag established, emphasis was placed on reducing the transonic drag. The drag problem included large afterbody and nozzle drag components

caused by high closure slopes (rapid variations in external aircraft contours), high drag

components of the cockpit and inlets, and very high boundary-layer spillage drag.

Dr. Richard T. Whitcomb and his staff conducted exhaustive tests of engine alignment,

wing and tail twist, and even antishock bodies to reduce drag. Studies by Ayers concluded that the area ruling for the F-111 was unsatisfactory.

Also in 1963, an F-111 aerodynamic consulting group consisting of Air Force, Navy,

and NASA members met and concluded that the transonic aerodynamic performance of

the F-111 would be considerably below the requirements for the projected missions.

Calculations based on Ayers’ drag measurements predicted that the aircraft would only

have a range of about 20 to 30 n mi for flight at low altitudes and speeds of a Mach number of 1.2, in contrast to the 220 n mi capability predicted by General Dynamics. Actual

flight tests later verified Ayers’ projection. The group, which included Polhamus and

Spearman, recommended that aft-end modifications suggested by Langley should be

studied for transonic drag reduction.

As concern over the aerodynamic performance of the F-111 increased, Charles Donlan

and Edward Polhamus briefed the Assistant Secretary of the Air Force in April 1964 on

the situation. They recommended that the staff of the Langley 16-Foot Transonic Tunnel

define the benefits of Langley conceived aft-end modifications. It was also suggested

that the wing with the longer span of the Navy aircraft be used on the Air Force aircraft.

Polhamus and Spearman also briefed Air Force General Schreiver and Navy Admiral

Schoech a month later on the transonic drag problem.

During May 1965, representatives of Grumman visited Langley several times to discuss

methods of improving the acceleration and maneuverability of the Navy F-111B.

Modifications considered by Grumman included several of the early Langley suggestions, such as a modified wing and pivot location, a straightened tailpipe, and an

improved interengine fairing. In addition, Grumman examined a modified horizontal

tail, alternate missile arrangements, and an aft-fuselage modification. Although these

modifications never came to fruition for the F-111B, the discussions had a large impact
Langley Contributions to the F-111

70 General Dynamics F-111 Aardvark

on the later design of the F-14 by Grumman, which became an outstanding Navy

aircraft.

Langley also assessed the effect of the bomb bay cavity and doors on directional stability in the Unitary Plan Wind Tunnel; the impact of missile carriage at supersonic speeds

in the Unitary Plan Wind Tunnel; the aerodynamic damping during subsonic, transonic,

and supersonic flight in the 30- by 60-Foot (Full-Scale) Tunnel, the Unitary Plan Wind

Tunnel, and the 8-Foot Transonic Pressure Tunnel; the transonic and supersonic flight of

the strategic bomber (FB-111) and reconnaissance (RF-111) versions of the F-111 in

these same wind tunnels; and the development of the F-111B by the Navy, until it was

cancelled on July 10, 1968. Over 25 test entries in the Unitary Plan Wind Tunnel were

made for the F-111 variants.

Propulsion Integration Hot-jet tests of a 1/9-scale ejector nozzle at transonic speeds were conducted in April

1963 in the Langley 16-Foot Transonic Tunnel to begin what would become an

extensive series of F-111 propulsion integration studies. (The staff ultimately conducted 17 entries of F-111 models or components during the program.) Later that year, a

1/6-scale inlet model was tested to determine the effects of aircraft nose shape (Air

Force and Navy) and engine inlet spike configuration. Following this test entry, the inlet,

cowl, and spike geometry were revised.

In 1964, General Dynamics, in consultation with the 16-Foot Transonic Tunnel staff,

completed fabrication of a 1/12-scale model designed to investigate propulsion-airframe

integration characteristics. This model represented the most realistic and complex

model of a military fighter ever tested in the 16-Foot Transonic Tunnel. The model had

multiple strain-gage balances and balance arrangements to independently measure

thrust, drag, and thrust minus drag. It also contained three independently controlled

internal flows to simulate the F-111 blow-in-door ejector exhaust system: a hot hydrogen peroxide primary-jet flow system, a high-pressure air secondary-flow system, and a

low-pressure air boundary-layer bleed system. In addition, the model contained fully

variable, aerodynamically actuated blow-in doors and ejector shroud flaps on the nozzles. Tests in 1964 on this model in the 16-Foot Transonic Tunnel indicated a significant

nozzle-thrust deficiency that was associated with an adverse fuselage afterbody flow

field. At the end of the year, additional tests of the hot-jet model were directed at a wide

range of ejector nozzle geometries in an attempt to solve nozzle-thrust and flutter problems. Langley also initiated studies directed toward reducing the large base drag associated with the short interengine fairing (interfairing). Relatively large drag improvements

were obtained with a long interfairing design conceived by Langley.

Unfortunately, the naval F-111B configuration was too long to met the requirements for

aircraft carrier elevator spotting (compatibility of the aircraft dimensions with the elevator on the aircraft carrier that transports aircraft to and from the flight deck and the lower

hangar area). Follow-on tests of the 1/6-scale inlet model during 1964 included studies

of the effects of an extended nose (for the RF-111), a weapons bay pod, and bleed doors.

Jack Runckel and Edward Polhamus briefed Air Force management in October 1964 on

the ejector nozzle problems of the F-111. Since the nozzle problem was associated with

the aircraft aft-end flow field and since the aft-end drag was relatively high, the Langley

representatives recommended that improvements to the back end of the aircraft be

investigated as a high priority item. Runckel subsequently became a key figure in a joint

F-111 nozzle committee that included the F-111 SPO, the Bureau of Naval Weapons,

Pratt and Whitney, General Dynamics, and NASA. In a meeting of this committee in
Langley Contributions to the F-111

General Dynamics F-111 Aardvark 71

January 1965, Runckel proposed that a truncated, concave base interfairing be investigated as a means of reducing drag at transonic speeds, while still meeting the length

restriction imposed by the F-111B naval version.

In February 1965, tests of the 1/12-scale hot-jet model indicated large improvements in

transonic performance because of airframe changes in the region between the nozzles.

This model configuration had the best aerodynamic characteristics to date in the program. A few months later, a meeting was held at Langley with representatives from the

F-111 SPO, the Bureau of Naval Weapons, General Dynamics, Grumman, Pratt and

Whitney, and Langley. At that meeting, it was agreed that emphasis should quickly

move to reducing transonic drag by developing an optimum engine interfairing and

speed bumps (additional area added to shape the aircraft to comply with Whitcomb’s

area rule). In December 1965, the hot-jet model was tested to develop the interfairing

and define a configuration that would be flight tested in early 1966. The aft-end modifications from this effort were ultimately adopted and resulted in a significant improvement in transonic drag.

The early F-111A exhibited numerous engine problems, including compressor surge

and stalls. NASA was a participant in finding solutions to these problems, as its pilots

and engineers flew test flights of the aircraft to determine inlet pressure fluctuations

(dynamics) that led to these events. Eventually, as a result of NASA, Air Force, and

General Dynamics studies, the engine problems were solved by a major inlet redesign.

The F-111 program brought many difficult challenges in propulsion-airframe integration to the staff of the Langley 16-Foot Transonic Tunnel. These problems were

extremely complex and demanded timely solutions in a highly visible, controversial

national program. However, the staff responded with outstanding technical expertise and

innovation. By the end of 1967, 19 F-111 related model entries had been completed in

the 16-Foot Transonic Tunnel, and over 283 configurations were investigated during

12.5 months of tunnel occupancy. This effort ultimately required participation of almost

every 16-Foot Transonic Tunnel staff member. Staff members who made significant

Inlet tests of an F-111 model in the Langley 16-Foot Transonic Tunnel.
Langley Contributions to the F-111

72 General Dynamics F-111 Aardvark

contributions to the F-111 program included Richard J. Re, Odis C. Pendergraft, Jr.,

Richard G. Wilmoth, Charles E. Mercer, Francis J. Capone, and Bobby L. Berrier. As a

result of the F-111 program, the research capability on aft-end transonic drag problems

greatly increased. This research capability contributed to all subsequent highperformance military aircraft and placed Langley in a position of world leadership in

this critical technical area.

High-Angle-of-Attack 

Characteristics

Initial free-flight model tests of the F-111 configuration were led by Peter C. Boisseau

in the Langley 30- by 60-Foot (Full-Scale) Tunnel in October 1964. During the flight

tests, the wing sweep was varied from 16 deg to 72.5 deg. In December, the model was

flown to determine the effects of stability augmentation in roll and pitch for the clean

and landing configurations. The flight tests were extended to high angles of attack,

including the stall.

When the model was flown to high angles of attack with the wings at the 50-deg and

72.5-deg sweep conditions, the model exhibited a sudden, uncontrollable yaw divergence prior to maximum lift. General Dynamics personnel, including the test pilot who

was scheduled to make the first high-angle-of-attack flights with the aircraft, witnessed

the tests.

The model free-flight tests also indicated an unusual unsteadiness in lateral behavior at

moderate angles of attack for the landing configuration. The unsteadiness was

apparently caused by an unsteady flow off the wing root glove (the fixed, highly swept

inner wing). In early 1965, extensive flow visualization tests were made in the Langley

12-Foot Low-Speed Tunnel in an effort to change the vortex-flow field set up by the

glove and to delay separation on the inner wing for the landing configuration. This work

Time-lapse photograph of the F-111A free-flight model at several

wings sweep angles during tests in the Langley Full-Scale Tunnel.
Langley Contributions to the F-111

General Dynamics F-111 Aardvark 73

included an investigation of a rotating glove vane, which was then evaluated during the

free-flight model test in the Full-Scale Tunnel. The glove vane cured the roll unsteadiness previously noted and was subsequently incorporated into the F-111 landing

configuration.

As F-111 operations expanded within the Air Force in the late 1960’s, a rash of incidents involving unexpected departures from controlled flight during maneuvers at high

angles of attack occurred. The Air Force requested industry and NASA assistance in

analyzing and solving the problem, which was viewed as a significant flight safety issue.

Langley researchers Joseph R. Chambers and James S. Bowman, Jr. served on an Air

Force, industry, and NASA committee that identified a shortcoming in the F-111 flight

control system that promoted the unintentional departures. The F-111 had been

designed with a g-command flight control system that provided g-forces in direct proportion to the deflection of the pilot control stick. However, in providing the pilot with

the level of g-force, the system would increase the angle of attack of the aircraft. Unless

the pilot was monitoring the angle of attack, the aircraft could enter a range of high

angles of attack where a loss of directional stability resulted in an unintentional yaw

departure and spin entry. These findings led to an Air Force program in 1973 to develop

a stall inhibitor system (SIS) for the F-111. Langley participated in the design and analysis of this system. The SIS was designed to automatically monitor and limit the angle

of attack of the aircraft during flight maneuvers and was incorporated into the F-111

fleet.

Spin Recovery Another area of controversy within the F-111 development program arose in the early

1960’s—in the area of spin and spin recovery technology. The conventional approach to

assessing and improving spin characteristics of new military aircraft was to conduct

tests of dynamically scaled models in the Langley 20-Foot Vertical Spin Tunnel to determine spin and spin recovery characteristics, as well as the size of the emergency parachute required for spin test aircraft. In conjunction with these tests, radio-controlled

drop-model tests were conducted to assess spin-entry tendencies and to assess the effectiveness of out-of-control recovery procedures.

For the F-111 program, General Dynamics proposed to assess spin recovery characteristics with analytical methods, in lieu of the traditional dynamic scale model tests. In

addition, General Dynamics requested over 1,000 hr in Langley tunnels to provide the

data required for the proposed study. Langley’s reaction to this proposal was extremely

negative because analytical procedures for spin studies had not been validated, and in

the opinion of James Bowman and the Spin Tunnel staff, could not be trusted for such

an important aircraft program. However, the Air Force accepted Langley’s recommendation to terminate the General Dynamics plans for the analytical approach and elected

to continue with the traditional Spin Tunnel and drop-model tests.

At the request of Langley, a 1/24-scale model of the F-111 was tested in the Ames

12-Foot Pressure Tunnel in early 1964 to examine Reynolds number effects at high

angles of attack and sideslip. The results of these tests necessitated forebody modifications for the spin tunnel model to simulate, at the low Reynolds numbers of spin tunnel

investigations, the cross-flow characteristics approximating the Reynolds number conditions of full-scale flight.

During the period from October 1964 to May 1966, extensive spin tunnel tests were

made by James Bowman and Louis White on 1/40-scale models of the F-111A and

F-111B aircraft to determine spin and recovery characteristics. Tests were conducted for
Langley Contributions to the F-111

74 General Dynamics F-111 Aardvark

wing-sweep angles of 20 deg, 26 deg, 50 deg, and 72.5 deg. The results of the tunnel

tests indicated that the F-111 would exhibit several spin modes, including steep oscillatory spins from which recovery could be accomplished and a fast flat spin from which

recovery was marginal or impossible using aerodynamic controls. The flat spin was

especially stable. A number of radical approaches to breaking the spin were attempted,

including sweeping the wings forward and rearward during the spin. For these tests, the

model was equipped with a small electric motor that was remotely actuated to drive the

wing-sweep angle. However, the flat spin could not be slowed or stopped using this

technique. All of these spins (including the flat spin) were subsequently encountered in

F-111 spin tests at Edwards Air Force Base and in fleet operations. Bowman served on

several spin accident investigation committees formed by the Air Force.

Extensive studies were made of the spin entry and post-stall motions of the F-111A by

Charles E. Libbey with two 1/9-scale helicopter drop models. Over 50 successful drops

were made with wing sweeps varying from 16 deg to 72.5 deg. Results of these tests

showed that certain pilot inputs following the yaw departure at high angles of attack (as

previously discussed for the wind-tunnel free-flight model) would promote the fast flat

spin. These results were discussed with Air Force representatives for inclusion in the

pilot handbook procedures for avoiding this extremely dangerous condition.

Several F-111 aircraft were lost in spin accidents during fleet operations; however, the

subsequent implementation of the SIS prevented stalls and eliminated spins as an operational concern.

During the late 1960’s, Langley researcher William P. Gilbert conducted fundamental

research on automatic spin prevention systems for fighter aircraft. Gilbert’s work was

stimulated by the fact that flight control systems were beginning to use flight parameters

(such as angle of attack and yaw rate) that would permit the mechanization of spin prevention for routine operations in highly redundant systems. Previously, the concept of

The F-111A drop model prior to launch from a helicopter for a spin-entry test.
Langley Contributions to the F-111

General Dynamics F-111 Aardvark 75

automatic spin prevention was a highly desirable concept, but the mechanization would

have required a special system that might be prone to failure and would only be utilized

on very rare occasions. With the emergence of the new operational control system components, Gilbert became interested in demonstrating the effectiveness of spin prevention

systems. Following a series of analytical studies, Gilbert teamed with Charles Libbey to

implement and test the prototype system on an F-111 drop model. With the system

engaged, the spin-prone model could be maneuvered to extreme angles of attack without entering a spin, even with full prospin control inputs from the pilot.

On one occasion, Gilbert briefed NASA Administrator, Dr. James Fletcher, on the very

positive results of his study. Fletcher praised the work as a forerunner of future systems

that would enable carefree maneuvering of military aircraft. Gilbert’s work with the

F-111 model represented one of the first efforts to develop the highly sophisticated control systems that are now used in virtually every domestic and foreign fighter aircraft to

prevent spins during strenuous air combat maneuvers.

Flutter Tests In early 1963, flutter trend models were tested in the Langley 26-Inch Transonic Blowdown Tunnel to determine the general flutter boundary for the isolated wing and tail surfaces of the F-111. Several tests were conducted in this facility, before a dummy

(stability) model of the complete F-111 configuration was tested in the Langley 16-Foot

Transonic Dynamics Tunnel (TDT) in August 1963. The initial TDT tests were to check

out the wind-tunnel suspension system for future flutter tests. Subsequent tests of the

isolated wing and horizontal tail in the Blowdown Tunnel revealed that the horizontaltail design had an inadequate margin of safety for flutter at low supersonic speeds, and

the geometry of the F-111 tail configuration was changed.

Flutter clearance tests of the F-111 empennage model and a 1/8-scale complete flutter

model of the F-111 were made in the TDT during February 1965. Flutter tests continued

through 1965 and subsequent years to examine the effects of a number of external store

configurations on flutter boundary. External stores for the F-111 included combinations

F-111 model in the Langley 16-Foot Transonic Dynamics Tunnel

in 1963. (Tail surfaces were later changed to avoid flutter.)
Langley Contributions to the F-111

76 General Dynamics F-111 Aardvark

of bombs, missiles, and fuel tanks. The wing pylons pivoted as the wings swept back,

keeping the ordnance parallel to the fuselage. F-111 tests led by Charles L. Ruhlin,

Maynard Sandford, and Irving Abel ultimately included 13 test entries in the TDT of

versions such as the F-111A, F-111B, and FB-111.

Crew Escape Module The two crew members in the F-111 sat side by side in an air conditioned, pressurized

cockpit module that served as an emergency escape vehicle and a survival shelter on

land or in water. In emergencies, crew members remained in the cockpit, an explosive

cutting cord separated the cockpit module from the aircraft, small rocket engines ejected

the module from the aircraft, and the module descended by parachute. The ejected module included a small portion of the inner wing glove to stabilize it during aircraft separation. Air bags cushioned the landing impact and helped to keep the module afloat in

water. After separation, the air bags were inflated with nitrogen (stored behind the

pilot’s seat).

The module could be released at any speed or altitude—even under water. For underwater escape, the air bags raised the module to the surface after it had been severed from

the plane. Initial concerns for the module design centered on potential windblast; however, this threat was properly addressed in the design. Unfortunately, impact of the level

of acceleration on the crew during landing proved to be a problem. The nominal descent

rate of the module on the parachute was about 32 ft/sec.

As a result of a number of back injuries to crew members during use of the recovery system and undesirable postimpact overturning, the Air Force requested that the NASA

Crash Dynamics Group conduct drop tests of the F-111 crew escape module at the

unique Langley Impact Dynamics Research Facility (IDRF). The facility had initially

been used to train astronauts for moon walks as part of the Apollo Program, when it was

known as the Lunar Landing Training Facility. After the successful Apollo Program, the

Langley staff recognized the value of the tall, large gantry structure for simulating

ground impact of large aircraft structures and full-scale general aviation aircraft and

rotorcraft. The Air Force provided F-111 crew escape modules and air bags for the tests

that were conducted at the facility.

FB-111 flutter model illustrating the wide scope of

external stores that were tested in the program.
Langley Contributions to the F-111

General Dynamics F-111 Aardvark 77

Huey D. Carden and Lisa E. Jones led the F-111 module tests at Langley. The tests

(between 60 to 70 drops) spanned from the early 1980’s to 1995. The objectives of the

tests were to assess

• Impact loads that were generated by the air bag attenuation system

• Structural loads that were transmitted to the seats and occupants

• Module stability under various impact attitudes which could exist due to drift from 

winds

• Design changes to the air bag attenuation system or seats.

Tests with controlled pitch, yaw, and roll orientations of the module relative to the forward velocity vector were conducted to account for various attitude envelopes of the

module during descent. Additional vertical tests were also performed. Impact velocities,

structural impact loads, air bag pressures, and loads transmitted to the seats and dummies representing the crew were measured and provided to the Air Force for

assessment.

Additionally, impact and postimpact behavior of the module was provided via extensive

onboard and ground-based cameras, which also provided module stability information.

The last series of drop tests in 1995 assessed the performance of and qualified an

entirely new air bag design that was required for a new parachute design.

The results of the Langley tests were analyzed and provided to the Air Force and the

industry contractor for continual refinement of the system. As a result of the data provided to the Air Force, load attenuating crew seats were included in the F-111 and air

bag and blowout plug design changes were made in the original air bags. Various

changes to the module led to the design of a new air bag system, which was tested for

qualification on the F-111 in the final series of tests prior to the retirement of the U.S.

F-111 fleet.

F-111 crew escape module during tests at the

Langley Impact Dynamics Research Facility.
Langley Contributions to the F-111

78 General Dynamics F-111 Aardvark

Wing Box Problems The F-111 airframe utilized a significant amount of high-strength D6ac steel in the wing

carry-through structure. This component was heat treated to a tensile strength of

220,000 psi and designed for -3g to 7.33g with design flight life goals of 4,000 hr and

10 years of service. However, a full-scale static test program that was conducted over a

6-year period encountered several failures, including a failure at the wing-pivot fitting.

Various modifications, including the first use of an advanced boron-reinforced composite doubler to reduce stress levels, coupled with an extension of the structural tests to

40,000 hr, were believed to have provided for 10,000 hr of safe operations.

In December 1969, an F-111 experienced a catastrophic wing failure during a pull-up

from a simulated bombing run at Nellis Air Force Base. This aircraft only had about

100 hr of flight time when the wing failed. The failure originated from a fatigue crack,

which had emanated from a sharp-edged forging defect in the wing-pivot fitting. As a

result of the accident, the Air Force convened several special committees to investigate

the failure and recommend a recovery program. James C. Newman, Jr. and Herbert F.

Hardrath represented Langley on the recovery team deliberations, and along with

Charles M. Hudson and Wolf Elber, they conducted fatigue crack growth and fracture

tests on specimens made from the D6ac steel used in the aircraft. These tests were conducted in the Langley Fatigue and Fracture Laboratory under conditions that simulated

aircraft operations. The original material had low fracture toughness due to the heattreatment process. The committee recommended that every F-111 be subjected to a lowtemperature proof test. This proof-test concept had been developed and successfully

used in the Apollo program, as well as other missile and space efforts. To screen out the

smallest possible flaw size, the F-111 full-scale proof tests were conducted at temperatures of about -40 ̊ F, where the fracture toughness of the D6ac steel was lower than the

fracture toughness at room temperature. The heat-treatment process was also corrected

to provide improved toughness for the D6ac material in newer aircraft. A decade later,

the same material with improved toughness was also successfully used in the Space

Shuttle solid rocket boosters. As a result of the revised proof-test approach and the

improved toughness material, there were no F-111 aircraft lost due to structural failure

in almost 30 years of operations before the aircraft was retired from service in 1996.

The F-111 failure was most responsible for the U.S. Air Force developing the damagetolerant design concept, where flaws, such as a 0.05-in. crack, are assumed to exist in

critical aircraft components. The structural components must then be tolerant of these

defects during flight conditions. This concept relies on fatigue crack growth and fracture

criteria to establish an inspection interval to insure the safety and reliability of the

aircraft.

The Transonic Aircraft 

Technology (TACT) Program

Richard Whitcomb’s pioneering research and development efforts on supercritical airfoils for enhanced transonic performance, which began at Langley in 1964 and continued until the 1980’s, included extensive wind-tunnel and flight evaluations for potential

military applications. After flight tests of a modified F-8 Crusader validated the benefits

of supercritical wing technology that had been predicted by theory and wind-tunnel

experiments for potential civil applications, NASA and the Air Force became interested

in assessing the benefits of supercritical wing applications to high-performance aircraft

during transonic maneuvers. Significant increases in the drag-divergence Mach number,

the maximum lift coefficient for buffet onset, and the Mach number for buffet onset at a

given lift coefficient were demonstrated for the supercritical airfoil when compared with

a NACA 6-series airfoil of comparable thickness. Theodore Ayers, in cooperation with

General Dynamics, conducted exploratory tests in the Langley 8-Foot Transonic
Langley Contributions to the F-111

General Dynamics F-111 Aardvark 79

Pressure Tunnel in 1966 to test the effects of a slotted supercritical airfoil on a

1/15-scale model of the F-111 with the existing flap system. Although the overall results

were not satisfactory because of high subcritical drag levels, the results encouraged

additional studies of an integral or unslotted supercritical airfoil. Tests of a 1/24-scale

F-111 model showed significant benefits to drag-divergence Mach number, maneuver

drag, and buffet onset characteristics. These tests also spurred additional interest by

General Dynamics in potential improvements of the F-111.

Following these exploratory tests at Langley, interest in supercritical applications continued to increase and a joint NASA and Air Force study that included ground and flight

activities was proposed. Specific objectives of the study included the effects of supercritical wings on transonic drag, buffet onset and magnitude, and handling qualities. In a

study known as the Transonic Aircraft Technology (TACT) Program, several candidate

military aircraft were examined for potential modifications to provide flight validation

of supercritical wing military applications.

The program was ultimately based on the application of supercritical technology to the

F-111 configuration, which had outer wing panels that could be relatively easily

replaced with modified supercritical sections. In addition, the potential retrofit of

advanced wings to enhance performance of the F-111 fleet was an interest in some areas

of the Air Force. The TACT Program, which started in 1969, included NASA Langley,

Dryden, and Ames Research Centers, and the Air Force Flight Dynamics Laboratory.

Theodore Ayers served as the Langley focal point for TACT activities, which included

extensive experimental development work of the modified wing in the 8-Foot Transonic

Pressure Tunnel by Ayers and James B. Hallissy (with considerable oversight and participation from Dr. Whitcomb), tests of a propulsion model in 1973 in the 16-Foot Transonic Tunnel by Charles Mercer, and flutter tests led by Charles Ruhlin and Maynard

Sandford in 1971 in the 16-Foot Transonic Dynamics Tunnel.

James B. Hallissy inspects the F-111 TACT model in

the Langley 8-Foot Transonic Pressure Tunnel.

F-111 TACT model in the Langley Unitary

Plan Wind Tunnel for supersonic tests.
Langley Contributions to the F-111

80 General Dynamics F-111 Aardvark

The F-111 TACT aircraft began flight tests at Dryden in 1972. Flight-test results showed

that the supercritical wing generated up to 50 percent more lift during maneuvers than

the conventional F-111 wing and significantly delayed the onset of wing buffet to higher

angles of attack. Special flight tests were also conducted to demonstrate that the carriage

of external stores on the wing pylons did not significantly degrade the benefits of the

supercritical wing. Although the Air Force decided not to retrofit the F-111 fleet, the

supercritical wing technology had dramatically demonstrated its benefits for incorporation into future military aircraft.

F-111 TACT model mounted for flutter tests in the Langley

16-Foot Transonic Dynamics Tunnel in 1971.

The NASA and Air Force F-111 TACT aircraft during flight tests at Dryden.
Langley Contributions to the F-111

General Dynamics F-111 Aardvark 81

The Mission Adaptive Wing 

(MAW) Program

In 1976, Theodore Ayers transferred from Langley to Dryden, where he accepted a position as Director for Aerodynamics. Ayers continued his interest in advanced wing configurations. Working with his technical peers within NASA, DOD, and industry, he

advocated for another important flight program with the modified F-111 at Dryden.

After the TACT Program ended in the 1980’s, the Air Force and NASA engaged in a

new technology development program known as Advanced Fighter Technology Integration (AFTI). One element of this joint program was the modification and flight tests of

the F-111 TACT aircraft with a Mission Adaptive Wing (MAW). The MAW used flexible wing skin and internal hydraulic control mechanisms to recontour the wing shape as

a smooth variable-camber wing for varying flight conditions. The objective was to provide the technical confidence for significant performance improvements with a wing

system that varied the wing contour in flight as a function of pilot inputs, flight conditions, and structural loads. The wing box of the existing TACT aircraft was equipped

with flexible wing leading and trailing edges. A high-lift section was used for low-speed

landing conditions, and the wing was recontoured to a supercritical shape for transonic

flight and adjusted to a symmetrical section for supersonic flight. Boeing, Grumman,

and General Dynamics bid on the request for proposals for the aircraft modification.

Tests of the competing configurations in the 8-Foot Transonic Pressure Tunnel were

conducted by James Hallissy. Boeing was awarded the contract in 1979. The MAW Program was managed by the Flight Dynamics Laboratory of the Air Force Wright Aeronautical Laboratories with Dryden as the responsible flight-test organization. Langley

supported this activity with exploratory tests of smooth variable-camber concepts in the

8-Foot Transonic Pressure Tunnel, which were conducted by James C. Ferris. Langley

also actively participated in the flight-test program, including conducting additional

tests with a 1/24-scale model. Langley personnel were also assigned temporarily at

Dryden during the flight program. The F-111 MAW flight research was conducted from

1985 to 1988 and included an assessment of automatic camber modes.

The F-111 Mission Adaptive Wing (MAW) aircraft during flight tests at Dryden.

Highlights of Research by Langley for the A-6

Grumman A-6 Intruder 83

Grumman A-6 Intruder

HIGHLIGHTS OF RESEARCH BY LANGLEY FOR THE A-6

1. Wind-tunnel studies of aerodynamic and thermal characteristics in the Langley 16-

Foot Transonic Tunnel provided data for selection of the configuration for the fuselage-mounted speed brakes.

2. Tests of A-6 configurations in the Langley 20-Foot Vertical Spin Tunnel determined

that spin recovery characteristics were significantly enhanced by enlarging the rudder and increasing the deflections of the horizontal tail and rudder.

3. Flutter clearance tests for a composite wing for the A-6E were successfully conducted in the Langley 16-Foot Transonic Dynamics Tunnel.

SPECIFICATIONS

Manufacturer

Grumman

Date in service

A-6A. . . . . . . . . . . . . . .1963

A-6E . . . . . . . . . . . . . . .1972

Type

Attack

Crew

Two

Engine

Pratt & Whitney J52-P8B

USERS

U.S. Navy and U.S. Marine 

Corps (retired in 1997)

DIMENSIONS

Wingspan. . . . . . . . . . . . 53.0 ft

Length . . . . . . . . . . . . . . 54.7 ft

Height . . . . . . . . . . . . . . 15.5 ft

Wing area. . . . . . . . . . .529 sq ft

WEIGHT

Empty . . . . . . . . . . . . 28,000 lb

Gross . . . . . . . . . . . . . 58,600 lb

PERFORMANCE

Max speed . . . . . . . . .563 knots
Highlights of Research by Langley for the A-6

84 Grumman A-6 Intruder

The Grumman (now Northrop Grumman) A-6 Intruder was an all-weather, two seat,

subsonic, carrier-based attack aircraft. Designed in the late 1950’s, the Intruder played a

critical role in the Vietnam War with over 35,000 combat sorties by 1973. The last version of the aircraft, the A-6E, was widely regarded as the best all-weather precision

bomber in the world. As an example of its effectiveness, during the strike on Libyan terrorist-related targets in 1986, A-6E Intruders penetrated sophisticated Libyan air

defense systems, which had been alerted by the high level of diplomatic tension and

rumors of impending attacks. Evading over 100 guided missiles, the strike force flew at

low altitude in complete darkness and accurately delivered laser-guided and other ordnance on target. Composite wing replacements and upgraded systems and weapons

improvement programs maintained the A-6’s combat capability until its retirement from

the fleet in early 1997.

Langley’s contributions to the A-6 Program began in 1959. Studies of the aerodynamic

and thermal characteristics of candidate designs for the fuselage-mounted speed brakes,

which were located adjacent to the hot efflux of the turbojet engines, were conducted in

the Langley 16-Foot Transonic Tunnel. Tests were also conducted in the 20-Foot Vertical Spin Tunnel to determine the spin and recovery characteristics of the aircraft and to

determine the size of parachute required for the spin test aircraft. Initial Langley tests

indicated that spin recoveries were significantly improved with an enlarged rudder and

more deflection angles for the horizontal tail and rudder. The rudder was enlarged, and

the control system was modified to provide the extended deflections. Follow-on spin

tests were also conducted over the years to determine the effects of new external stores

and new weapons on spin recovery characteristics.

Arguably, the most important contribution of Langley to the A-6 Program was a series

of two test entries in the Langley 16-Foot Transonic Dynamics Tunnel (TDT) to ensure

flutter clearance for an advanced composite wing that was incorporated into the A-6E

fleet to extend the fatigue life and capabilities of the aircraft. Initial tests in the TDT

ended in flutter failure of the model wing, but a revised wing design passed flutter demonstration requirements and permitted the fleet to utilize the advanced wing.
Langley Contributions to the A-6

Grumman A-6 Intruder 85

LANGLEY CONTRIBUTIONS TO THE A-6

Speed Brake Studies In May 1959, a team from Langley and Grumman led by Langley researcher Charles E.

Mercer conducted powered-model tests in the Langley 16-Foot Transonic Tunnel to

determine the optimum configuration for fuselage-mounted speed brakes–thrust spoilers

for the A-6 (then designated the A2F-1). The speed brake panels were located immediately behind the engine exhaust nozzles on the rear fuselage, which caused concern over

the aerodynamic loads and the thermal environment of the speed brakes during highpower conditions. To further complicate the engineering issues, the original aircraft also

had a tilting tailpipe to increase lift at low speeds and thereby reduce approach speeds.

The test examined several candidate configurations, including a perforated panel design,

which was subsequently incorporated into the early A-6A and EA-6A. Later variants of

the A-6 used symmetrically deflected split ailerons at the wingtips for speed brakes, and

the original speed brake panels were inactive or deleted.

The A-6 prototype made its first test flight in April 1960. The Navy was satisfied with

the 90-knot approach speed, so the deflectable nozzle design feature was eliminated in

production aircraft. The Langley staff, however, continued research on thrust vectoring,

which later contributed to more advanced fighter designs.

Spin Tunnel Tests Initial evaluations of the spin and spin recovery characteristics of the A-6 by Henry A.

Lee in the Langley 20-Foot Vertical Spin Tunnel indicated that spin recoveries could be

significantly enhanced by an enlarged rudder and by additional deflections of the rudder

and horizontal tail. The original A-6 design had incorporated extended throws on the

rudder and horizontal stabilizer for the power approach configuration, so an assist spin

recovery switch was installed so the pilot could extended deflections for the cruise

Powered-model tests in the Langley 16-Foot Transonic

Tunnel evaluated several speed brake configurations.
Langley Contributions to the A-6

86 Grumman A-6 Intruder

configuration. The Langley tests determined that the greater horizontal-tail deflection

angle (trailing-edge up) provided a better flow field on the vertical tail during spins,

thereby increasing the effectiveness of the rudder to terminate the spin. The rudder of

the production aircraft was enlarged as a result of these tests.

The Composite Wing By the mid-1980’s, the A-6 was beginning to show its age. The accumulated stress of

high-g catapulted takeoffs and arrested landings on carriers and the long exposure to salt

water were beginning to take a toll on the life of airframe components. Studies were

underway for a new wing design, and inspections of the A-6 structure revealed major

corrosion problems. In January 1987, a fatal accident resulted in an investigation of the

structural health and projected lifetime of the A-6 fleet (ref. 5).

At the time of the accident, U.S. Marine Corps First Lieutenant Bob Pandis and his

bombardier/navigator, Lieutenant Colonel John Cavin, were practicing dive-bombing

missions at the El Centro Naval Base in California. During a 40-deg diving run at about

500 knots, the left wing of their A-6E broke off the aircraft at an altitude of about

8,000 ft and the aircraft began to spin wildly out of control. When the wing separated

from the aircraft, fuel from the severed fuel cells in the aircraft immediately ignited in a

giant fireball, adding to the severity of the rolling motion. The violence of the roll

caused the empennage to separate from the aircraft, which started cartwheeling endover-end. Pandis ejected from the out-of-control aircraft and suffered major injuries,

while Cavin died in the crash.

Pandis later recalled that the two other A-6’s in his flight had noticed fuel venting from

his left wing during the run for the dive. About halfway into to the dive, the crews of the

two aircraft saw a dramatic increase in fuel venting and were shocked to see the left

wing tear off the aircraft.

Prior to this terrible accident, 72 A-6 aircraft had been temporarily grounded and

another 109 were operating under flight restrictions. The Boeing Company had begun

to design a new wing under a Navy contract that was awarded in 1985. With a

Flutter tests of the new A-6 composite wing in the Langley 16-Foot

Transonic Dynamics Tunnel included numerous external store loadings.
Langley Contributions to the A-6

Grumman A-6 Intruder 87

carbon fiber–epoxy resin torsion box, light alloy control surfaces, and some titanium

components, the new wing was much lighter and designed for four times the fatigue life

of the existing wing. In addition to becoming a retrofit for the A-6E fleet, the wing was

also intended for a new, advanced version of the A-6 to be known as the A-6F. (The

A-6F was later canceled in the prototype stage when the Navy decided to replace the

A-6 fleet with the stealth A-12 aircraft).

At the request of the Navy, tests were conducted in the Langley 16-Foot Transonic

Dynamics Tunnel (TDT) in February 1986, to ensure that the new wing would not

exhibit flutter within the flight envelope. The preflight flutter clearance tests required

two separate entries in the TDT under the leadership of Langley researchers Stanley R.

Cole and Jose A. Rivera, Jr. The first composite-wing model was lost in a catastrophic

flutter event while testing a “pencil” store configuration that represented the fuel tanks.

Pencil stores are slender metal rods that simulate the moments of inertia of the real fuel

tanks while minimizing aerodynamic effects. The test of the pencil store configuration is

part of the flutter clearance test; however, the result was much more severe flutter than

expected and the model was destroyed. Based in part on these results, Boeing modified

the structural design of the A-6 composite wing. A second model incorporating the new

wing design was fabricated and tested in the TDT in June 1987. This second model

demonstrated no flutter incidents within the scaled flight envelope plus a safety margin.

A unique aspect of both models was that they were semispan models (only one half of

the aircraft was modeled); however, Boeing designed a unique root constraint to simulate the carry-through structure of the wing at the fuselage. The semispan model was

larger than a full-span model, thereby permitting more accurate representation of the

structural characteristics at model scale. Also of interest with regard to model design,

the first model had a very clean wing surface. However, the decision was made to

include the bumps, fences, and other wing features that were present in the actual flight

hardware on the second model.

Subsequent to the Langley tests, the composite wing was retrofitted to about 200 A-6E

aircraft, which significantly increased the aircraft’s capability, safety, and operational

life.

By 1988, the team of McDonnell Douglas and General Dynamics began to build the A-6

replacement called the A-12 Avenger. Unfortunately, Defense Secretary Richard

Cheney cancelled the $57 billion project after cost overruns exceeded $2.7 billion dollars in the development phase. Nonetheless, the decision to retire the A-6 was

unchanged, and the F/A-18 Hornet became the replacement aircraft for the Intruder. The

last flight of the A-6 Intruder occurred in early 1997.

Highlights of Research by Langley for the EA-6B

Grumman EA-6B Prowler 89

Grumman EA-6B Prowler

HIGHLIGHTS OF RESEARCH BY LANGLEY FOR THE EA-6B

1. Tests in the Langley 20-Foot Vertical Spin Tunnel resulted in increased control surface deflections for spin recovery.

2. Langley cooperated with the Navy and Grumman to determine configuration modifications that significantly improved maneuver aerodynamics, high-angle-of-attack

characteristics, and low-speed high-lift capability.

3. Aft-fuselage ram-air cooling scoops were designed with data from tests in the

Langley 7- by 10-Foot High-Speed Tunnel.

SPECIFICATIONS

Manufacturer

Grumman

Date in service

1971

Type

Electronic warfare

Crew

Four

Engine

Pratt & Whitney J52-P-408A

USERS

U.S. Navy and U.S. Marine 

Corps

DIMENSIONS

Wingspan. . . . . . . . . . . . 53.0 ft

Length . . . . . . . . . . . . . . 59.8 ft

Height . . . . . . . . . . . . . . 16.3 ft

Wing area. . . . . . . . . . .529 sq ft

WEIGHT

Empty . . . . . . . . . . . . 34,300 lb

Gross . . . . . . . . . . . . . 61,500 lb

PERFORMANCE

Max speed . . . . . Mach number

of 0.72
Highlights of Research by Langley for the EA-6B

90 Grumman EA-6B Prowler

The Grumman (now Northrop Grumman) EA-6B Prowler is a unique national asset that

can be deployed from land bases and aircraft carriers to monitor the electromagnetic

spectrum and actively deny an adversary the use of radar and communications. This aircraft is included in every aircraft carrier deployment and has a primary mission to protect fleet surface units and other aircraft by jamming hostile radar and communications.

The EA-6B played a key role in suppressing enemy air defenses during Operation

Desert Storm for U.S. and allied forces. The Department of Defense (DOD) has now

assigned all radar jamming missions to the Prowler.

The EA-6B airframe is a derivative of the A-6E Intruder. Although the fuselage was

stretched to permit space for four crew members, the wing area is the same as that used

on the A-6E. The basic mission, external stores, and electronic suites of the Prowler are

considerably different from those of the A-6E. Also, the EA-6B is considerably heavier

than the A-6, which results in a significant reduction in maneuvering capability. As a

result of an alarming increase in accident rates for the EA-6B fleet in the early 1980’s,

the Navy requested support from Langley to define modifications that might improve

maneuver aerodynamics, high-angle-of-attack stability and control, and low-speed highlift systems. During follow-on Navy flight tests, these modifications to the wing airfoil,

vertical tail, wing leading and trailing edges, and roll control devices significantly

enhanced the capabilities of an EA-6B demonstrator aircraft. Langley also supported a

Navy and Grumman request to conduct wind-tunnel tests to define fuselage ram-air

cooling scoop concepts for additional aerodynamic cooling of electronic systems. The

significant improvements predicted by the results of Langley tests were verified during

Navy flight evaluations of a modified A-6F aircraft.

Langley facilities that supported the EA-6B program included the 20-Foot Vertical Spin

Tunnel, the National Transonic Facility (NTF), the 7- by 10-Foot High-Speed Tunnel,

the 16-Foot Transonic Tunnel, the 30- by 60-Foot (Full-Scale) Tunnel, the LowTurbulence Pressure Tunnel (LTPT), the 6- by 28-Inch Transonic Tunnel, and the

12-Foot Low-Speed Tunnel.
Langley Contributions to the EA-6B

Grumman EA-6B Prowler 91

LANGLEY CONTRIBUTIONS TO THE EA-6B

Spin Tunnel Tests The EA-6B aircraft is a four-seat, electronic warfare derivative of the A-6E Intruder.

The major external differences between the EA-6B and the two-seat A-6E are a 54-in.

fuselage extension for two additional crew stations, a large pod on the vertical tail to

house electronic countermeasures equipment, and a canted refueling probe. The EA-6B

is more than 10,000 lb heavier than the A-6E, and carries large pods for electronics on

wing pylons. In view of these significant configuration changes, the Navy requested that

Langley conduct tests to determine spin and recovery characteristics of the EA-6B.

Henry A. Lee and James S. Bowman, Jr. conducted the investigation in 1971.

As discussed in Langley Contributions to the A-6, a cockpit switch had been implemented in the A-6 to provide the pilot with the option of increasing horizontal-tail and

rudder deflections for spin recovery. The results of the tests of the EA-6B indicated that

the existing 23-deg rudder deflection was not sufficient for satisfactory spin recovery.

The rudder deflection on production aircraft was increased to 35 deg with the A-6 assist

spin recovery switch, which was also implemented on the EA-6B.

Maneuver Improvements The EA-6B has a significantly higher design gross weight than the A-6E; however, the

EA-6B employs the same wing to carry the increased load. This increased wing load

contributed to an alarming number of EA-6B accidents in the early 1980’s. During that

period the EA-6B aircraft experienced accident rates in fleet operations that were nearly

three times higher than all other Navy and Marine aircraft combined. The majority of

these mishaps were attributed to out-of-control flight and resulted in the loss of the aircraft after the pilots were unable to recover the aircraft and were forced to eject. These

losses prompted many fleet squadrons to restrict the EA-6B from intentional maneuvers

at high-angle-of-attack conditions. While the restrictions substantially reduced the accident rates, they also imposed constraints on evasive maneuvers while operating in high

threat environments.

In late 1984, the Navy approached Langley to undertake a research program to improve

the EA-6B, with emphasis on increasing maximum usable lift, maintaining lateraldirectional stability near stall, and maintaining lateral control near stall. Langley agreed

to lead this effort, under the cognizance of the Navy. Grumman joined the effort and

provided additional technical support to Langley, as well as participating in additional

wind-tunnel tests at NASA Ames Research Center for the high-lift configuration. This

program evaluated the EA-6B in ten NASA and Grumman facilities.

The modified EA-6B model in flight in the Full-Scale Tunnel.
Langley Contributions to the EA-6B

92 Grumman EA-6B Prowler

Langley research activities on the high-angle-of-attack stability and control characteristics of the EA-6B were led by Joseph L. Johnson, Jr. and his staff of the Low Speed

Aerodynamics Division. The efforts to improve maximum lift and maneuver performance were led by Percy J. (Bud) Bobbitt and his staff of the Transonic Aerodynamics

Division.

Johnson’s team conducted extensive tests in the Langley 12-Foot Low-Speed Tunnel

and the Langley 30- by 60-Foot (Full-Scale) Tunnel with flow visualization and force

and moment measurements. The Langley leaders in this effort were Frank L. Jordan, Jr.

and David E. Hahne. The results of these tests showed that the vertical tail was

adversely affected by flow emanating from the fuselage and wing root areas for highangle-of-attack conditions, which resulted in a severe loss of directional stability. The

problem was resolved by extending the vertical tail above the existing fin pod, adding

leading-edge droop to the inboard wing, and adding a strake to the wing-fuselage intersection. Roll control at high-angle-of-attack conditions was augmented by using the

existing wingtip speed brakes as additional ailerons. These modifications were tested

with a 0.12-scale free-flight model in the Full-Scale Tunnel. The results clearly demonstrated the potential of these modifications to improve the flight characteristics of the

EA-6B at high angles of attack.

Bobbitt’s team worked to improve maximum lift. This task was a challenge as changes

in wing contour were limited to the leading-edge slat and trailing-edge flap to keep retrofit costs low. Several advanced airfoil designs were tested by William G. Sewall,

Robert J. McGhee, and James C. Ferris in the Langley 6- by 28-Inch Transonic Tunnel

and in the Langley Low-Turbulence Pressure Tunnel (LTPT). The results of the airfoil

Langley researcher David E. Hahne with the EA-6B free-flight model.
Langley Contributions to the EA-6B

Grumman EA-6B Prowler 93

studies were used to design advanced slats and flaps for the EA-6B that produced a substantial increase in lift, as well as decreased drag at cruise Mach numbers. Edward G.

Waggoner and Dennis O. Allison led computational and experimental studies to design

the wing configurations to increase the low-speed maximum lift capability of the EA-6B

with minimal degradation in high-speed performance. Their work ranged from the

application of low-speed and transonic computational methods to experimental verification tests in the Langley 7- by 10-Foot High-Speed Tunnel and the National Transonic

Facility (NTF) at Langley. The integrated efforts of these two teams identified new

leading- and trailing-edge configurations that dramatically improved the high-lift performance of the EA-6B. The modifications defined by the Johnson and Bobbitt teams

were then tested on a model at Ames to assess the impact on the high-lift configuration.

Spin tunnel tests were also conducted to evaluate the impact of the changes on spin and

spin recovery characteristics. No degradation was noted during the tests, and the existing spin characteristics of the EA-6B were projected to remain unchanged. The final

tests included wing loads tests led by Langley researcher Charles Mercer in the Langley

16-Foot Transonic Tunnel. Tests of a full-size, EA-6B semispan wing in the Full-Scale

Tunnel led by Jordan and Hahne validated the effectiveness of using the speed brakes as

ailerons and provided additional loads data. Because the A-6E had significant problems

with fatigue life, it was important to assess the impact of the modifications on wing

loads and wing root bending moments to ensure that the EA-6B wing fatigue life would

not be degraded.

The impact of the Langley-led test program was substantial. Test data indicated the

potential for a 25-percent increase in maximum usable lift in the cruise configuration.

Lateral and directional stability could be maintained to angles of attack well beyond

stall. Lateral control could be maintained beyond stall by using the speed brakes as ailerons. A performance improvement due to decreased drag could be realized at medium

EA-6B model being prepared for tests in the National Transonic Facility at Langley.
Langley Contributions to the EA-6B

94 Grumman EA-6B Prowler

and high altitudes where a majority of the EA-6B missions are flown. Approach speeds

could be substantially reduced at existing landing gross weights, and growth capability

was provided for higher gross weights. Finally, an extensive, unprecedented aerodynamic database for the EA-6B had been produced and was ready for incorporation into

simulators for EA-6B pilot training.

The results of this outstanding NASA, Navy, and Grumman joint program were summarized in several technical papers in 1987. The effort received such positive national

attention that in the 1987 Applied Aerodynamics AIAA meeting, an entire session was

dedicated to the EA-6B effort with five papers presented. Aircraft modifications defined

by the joint EA-6B program were directed at an advanced version of the aircraft known

as the EA-6B ADVCAP (Advanced Capability), which included a myriad of improvements such as new engines and electronic upgrades, as well as the airframe modifications. Flight tests of a modified EA-6B designated the Vehicle Enhancement Program

(VEP) test aircraft were conducted to evaluate the effects of the airframe modifications

derived from the Langley-led joint studies. Flights began on June 15, 1992, and the final

flight occurred on April 4, 1994. The flight evaluation of the test aircraft validated all

projections of the research program, and the performance, stability, and control

characteristics of the modified aircraft were judged to be far superior to those of the

basic EA-6B. The aircraft performed flawlessly. Unfortunately, fiscal constraints and

other programmatic issues restrained the Navy from funding the upgrades. EA-6B simulators, however, have been upgraded with the data from Langley.

Cooling Study The continuing evolution of the EA-6B and the demands of the all-weather warfare mission involved a continuous upgrade of advanced electronic systems that demand adequate cooling for satisfactory operations. In particular, the projected Advanced

Capability (ADVCAP) version of the aircraft included a significant electronics upgrade

that required additional cooling. Langley participated in a joint NASA, Navy, and

Grumman wind-tunnel study of new aft-fuselage ram-air scoops to satisfy the cooling

requirements. Langley researcher William Sewall led these tests, which were conducted

in the Langley 7- by 10-Foot High-Speed Tunnel. The scoop configuration derived from

the tests was evaluated in flight tests of a prototype of another advanced A-6 derivative

known as the A-6F. The scoop configuration was to be included in the overall ADVCAP

package, which was not funded for continued development.

EA-6B Vehicle Enhancement Program (VEP)

test aircraft during flight evaluation.
Langley Contributions to the EA-6B

Grumman EA-6B Prowler 95

EA-6B fuselage and empennage model in the Langley 7- by

10-Foot High-Speed Tunnel for air scoop studies.

A-6F prototype with aft-fuselage scoops.

Highlights of Research by Langley for the F-14

Grumman F-14 Tomcat 97

Grumman F-14 Tomcat

HIGHLIGHTS OF RESEARCH BY LANGLEY FOR THE F-14

1. The F-14 employs the variable-sweep wing developed by Langley to meet wide

ranging mission requirements.

2. Langley conducted wind-tunnel tests to collect data for the competitive source selection team.

3. Langley personnel participated in the evaluation process.

4. At the request of the Department of Defense, Langley led a multidiscipline assessment of the F-14 in early development and reported the results to the Navy.

5. Langley conducted propulsion integration studies to improve the subsonic cruise

efficiency that resulted in a redesign of the aft end.

6. Langley studies of the high-angle-of-attack and spin characteristics identified a

potential flat spin and an innovative flight control system modification that dramatically reduced the spin susceptibility of the aircraft.

7. Tests in the Langley 16-Foot Transonic Dynamics Tunnel identified potential flutter

of the F-14 over-wing covers, which Grumman solved with external strake stiffeners.

8. Langley provides technology, expertise, and facility support on a continual basis,

such as providing numerical models for pilot training simulators.

SPECIFICATIONS

Manufacturer

Grumman

Date in service

November 1974

Type

Carrier-based multirole

Crew

Two

Engine

F-14B/D . . . General Electric 

F-110-GE-400 augmented 

turbofan with afterburner

USER

U.S. Navy

DIMENSIONS

Wingspan

unswept. . . . . . . . . . . 64.2 ft

swept. . . . . . . . . . . . . 38.2 ft

Length . . . . . . . . . . . . . . 61.9 ft

Height . . . . . . . . . . . . . . 16.0 ft

Wing area. . . . . . . . . . .565 sq ft

WEIGHT

Empty . . . . . . . . . . . . 41,700 lb

Max takeoff . . . . . . . . 74,349 lb

PERFORMANCE

Max speed . . . . . Mach number

of 2.3

Unrefueled

range . . . . . . . . . . . . 3,450 n mi
Highlights of Research by Langley for the F-14

98 Grumman F-14 Tomcat

The multirole F-14 fighter employs many Langley technical concepts that permit it to

accomplish diverse requirements such as supersonic dash and landing on an aircraft carrier in adverse conditions. Grumman relied on existing NASA databases and consultation during the design of the F-14. Langley staff tested and analyzed the competing

designs in the Navy Advanced Fighter (VFX) Program competition that resulted in the

F-14. Technical contributions to the F-14 from Langley include the areas of aerodynamic performance, high-angle-of-attack and spin characteristics, and flutter suppression. Langley facilities used in F-14 studies included the 30- by 60-Foot (Full-Scale)

Tunnel, the 20-Foot Vertical Spin Tunnel, the 4- by 4-Foot Supersonic Pressure Tunnel,

the 8-Foot Transonic Pressure Tunnel, the Unitary Plan Wind Tunnel, the 16-Foot Transonic Tunnel, the 16-Foot Transonic Dynamics Tunnel, the 7- by 10-Foot High-Speed

Tunnel, the Differential Maneuvering Simulator, and radio-controlled models dropped

from a helicopter. In addition, Langley provided leadership for high-angle-of-attack

F-14 flight experiments in a joint NASA, Navy, and Grumman program at NASA

Dryden Flight Research Center.

Following the selection of the Grumman design at the completion of the VFX Program,

the Department of Defense requested that NASA provide an independent assessment of

the F-14. A NASA team of 45 professionals that was led by Langley briefed their findings to the Navy and helped shape the development of the aircraft. Over 11,000 hr of

wind-tunnel tests were conducted in Langley facilities during the subsequent F-14

development program.
Langley Contributions to the F-14

Grumman F-14 Tomcat 99

LANGLEY CONTRIBUTIONS TO THE F-14

Early NASA Fighter Studies During the development of the variable-sweep wing at the Langley Research Center,

researchers recognized the advantages of applying the concept to multimission aircraft.

One ideal application was for naval fleet defense fighters, which must be able to quickly

intercept threats and yet slowly approach aircraft carriers to land. Variable-sweep wings

in the fully swept (high-speed) configuration permit efficient supersonic dash and the

carrier-approach requirements could be met with the wing in the unswept (low-speed)

position. Inspired by the potential of this application of variable-sweep technology,

Langley conducted several in-house studies of fighter configurations for naval applications. In 1967, Langley published the results of in-house studies of a variable-sweep

fighter configuration known as LFAX-4 that incorporated several features that are evident in the F-14 aircraft. Some of these features are

• Short propulsion package to minimize weight

• Engines placed forward for balance

• Horizontal ramp engine inlets for good performance at high angles of attack

• Tailored twin-engine aft-end spacing and interfairing for efficient subsonic cruise 

conditions

Results of studies of the performance, stability, and control characteristics of the

LFAX-4 obtained across the speed range of a representative advanced naval fighter were

outstanding, and Langley researchers conducted extensive briefings of their findings at

industry and Department of Defense (DOD) sites.

One result of the LFAX-4 study that the Langley team emphasized was the critical location of the pivot for the movable wing panels. To minimize drag during transonic

The Langley LFAX-4 fighter configuration.
Langley Contributions to the F-14

100 Grumman F-14 Tomcat

maneuvers typical of air-to-air combat, the pivots must be located in a relatively outboard position. Langley’s experience with the test and analysis of the F-111 revealed

that large penalties in trim drag occurred if this key design factor was not adequately

appreciated. Although the F-111 incorporated the variable-sweep concept, the full

advantages of the concept were not realized because the pivot locations were relatively

inboard. As a result, the F-111 suffered excessive trim drag at transonic and supersonic

conditions. The designers of the F-14 were made aware of the significance of pivot locations by NASA briefings. Comparison of the NASA results for the LFAX-4 to those of

the F-111 helped convince Grumman to locate the F-14 pivots in a more favorable outboard position.

The LFAX-4 studies also pointed out the importance of the placement of the horizontal

tail relative to the wing for stability and control. These recommendations were also

included in the F-14 design.

F-14 Source Selection Following the disastrous attempt to achieve interservice aircraft commonality with the

F-111, the Navy issued a request for proposals (RFP) for a new VFX fighter in July

1968. Competitors included Grumman, General Dynamics, Ling-Temco-Vought,

McDonnell Douglas, and North American Rockwell. At the request of the Navy, the

competing configurations were evaluated with wind-tunnel data from the Langley

8-Foot Transonic Pressure Tunnel, the 7- by 10-Foot High-Speed Tunnel, the Unitary

Plan Wind Tunnel, and the 16-Foot Transonic Tunnel. Langley personnel also participated in briefings of their results to the industry teams and the Navy.

NASA Independent Assessment On January 14, 1969, the Navy announced the award of the contract for the VFX fighter,

now designated F-14, to Grumman. The Assistant Secretary of the Navy requested that

NASA make a timely independent assessment of the technical development of the F-14.

A NASA F-14 Study Team of over 40 Langley personnel led by Langley researcher

William J. Alford, Jr. was organized. A briefing of the study results was given in August

1969 at the Naval Air Systems Command by a team led by Laurence K. Loftin, Jr.,

Mark R. Nichols, and William Alford. This briefing (which covered results in cruise and

maneuvering performance, aeroelasticity and flutter, propulsion integration, stability,

and control) identified several areas where further research would enhance the F-14’s

capabilities. Following the briefing, Dr. John Foster, Director of Defense Research and

Engineering, requested the support of Langley in the development of the F-14.

Propulsion Integration Initial flight-test evaluations of the performance of the F-14 by the Navy revealed higher

drag levels at high subsonic and transonic speeds than had been predicted by Grumman

wind-tunnel tests. The Navy requested Langley support in analyzing and providing solutions to the problem. Langley experience with the F-111 and other advanced fighter concepts indicated that an extremely large portion of the high subsonic and transonic cruise

drag of modern twin-engine fighters is contributed by the aft end of the configuration.

For example, a relatively poor aft-end design could produce almost 50 percent of the

cruise drag for some configurations. In the course of the F-111 development program,

Langley researchers in the 16-Foot Transonic Tunnel had developed test techniques and

analysis methods to minimize this problem, and they went to work on the aft-end aerodynamic characteristics of the F-14 configuration.
Langley Contributions to the F-14

Grumman F-14 Tomcat 101

Based on their extensive experience, the 16-Foot Transonic Tunnel team conducted tests

in 1972 to determine the characteristics of the critical engine-fuselage fairing (pancake)

at the rear of the aircraft. Several geometric variations were evaluated to determine more

effective pancake shapes, with an appreciation of the trades that are necessary to minimize component interference drag while adhering to the area rule developed by Langley

researcher Dr. Richard Whitcomb. In addition, certain regions had to be preserved for

the F-14 fuel jettison system and the landing arrestor hook. The researchers cut away

areas of the pancake, reshaped the geometry and added a “handle” in the shape of a bulbous pod at the rear of the pancake. The design recommended by the Langley tests

proved extremely effective in reducing cruise drag and was incorporated into the F-14

configuration.

In addition to the pancake modification, Langley researchers recommended that generous “speed bump” (area added to shape the aircraft to comply with Whitcomb’s area

rule) fairings be added to the forward bottom area of the vertical tails. The suggestion

was accepted by Grumman and incorporated into the production F-14 fleet.

Pancake configurations evaluated in cruise-drag studies in the

Langley 16-Foot Transonic Tunnel. Original shape is at left.

Aft-end pancake handle and vertical tail root speed bumps on F-14 aircraft.
Langley Contributions to the F-14

102 Grumman F-14 Tomcat

High-Angle-Of-Attack and 

Spin Research

In early 1970, initial tests conducted in the Langley 20-Foot Vertical Spin Tunnel at the

request of the Navy indicated that the F-14 would exhibit two types of spins. The first

spin involved relatively steep, nose-down spins from which recovery would be relatively

easy for the pilot. However, the results also showed that the F-14 might exhibit a relatively flat unrecoverable spin in which the aircraft would rotate rapidly (2 sec per turn)

about a vertical axis through its center of gravity, while descending vertically with the

fuselage in a relatively horizontal attitude. Because of the high rate of rotation of the flat

spin, the g-forces at the cockpit location would be very high (approximately 6.5 longitudinal g’s outward) and would probably incapacitate the pilot if sustained for even a

moderate period of time. Under the direction of Langley researcher James S. Bowman,

Jr. exhaustive spin tunnel tests were conducted to define a spin recovery procedure, but

the aerodynamic control surfaces of the F-14 were ineffective at these flat attitudes. In

fact, even a scaled version of a very large 35-ft diameter spin recovery parachute (the

largest that could be carried by the F-14 was 21 ft) could not recover the model from the

spinning motions. The only concept that provided marginal recovery was the simultaneous application of normal recovery controls, deployment of the emergency parachute,

and extension of auxiliary canards on the nose of the model.

Unrecoverable flat spins have been exhibited by many fighter configurations in the

Langley Spin Tunnel, and such characteristics are viewed with concern. However, additional types of model tests are required to judge the seriousness of the problem. In particular, drop-model tests are conducted to determine if the aircraft can enter the spin

from initial flight conditions. Spin tunnel tests are conducted with the model launched in

a flat attitude into a vertically rising airstream—conditions very favorable for the spin to

stabilize. However, in actual flight conditions, many aircraft lack the control power

required to reach these conditions. For example, although the F-5 aircraft exhibited a flat

spin in Langley Spin Tunnel tests, it was virtually impossible for pilots to intentionally

enter the flat spin.

F-14 model in spin recovery tests in the Langley Spin Tunnel.
Langley Contributions to the F-14

Grumman F-14 Tomcat 103

Two F-14 drop models were under fabrication when the spin tunnel results became

known. The Langley, Grumman, and Navy team had planned to equip the models with

extensive instrumentation to measure flight variables for correlation with analytical

studies of the spin, but the installation process would have taken several months.

Because the Navy required an immediate answer about the susceptibility of the F-14 to

enter flat spins, Marion O. McKinney directed the team to install limited instrumentation in one of the models, and to obtain answers as quickly as possible. With the

approval of this approach by the Navy, Charles E. Libbey and his team installed a miniature movie camera in the engine inlet of the model and pointed it forward, where it

could monitor the relative angle of a simple wooden angle-of-attack vane mounted on a

nose boom. This innovative approach gave the Navy answers in a few weeks, rather than

months. The team conducted as many as 4 drop tests a day in a very successful test

series. More refined instrumented model tests were completed later for a total of 55 drop

tests in the program.

Libbey and his team concentrated their initial studies on the susceptibility of the F-14

model to enter the spin by manipulating the controls after the model had been dropped

from a helicopter. Results of the tests showed that the model could be pitched up in an

aggressive manner with no tendency to enter either the steep or flat spins. However, if

the roll control (differential deflection of the horizontal tails) was used in normal fashion

to pick up a down-going wing at high angles of attack, the model would depart controlled flight in a direction opposite of the intended input because of adverse yaw caused

by large yawing moments produced by the horizontal tails. If the pilot held in the roll

control, the model would enter a flat spin. Recovery from flat spins requires the use of

an emergency parachute, special nose canards, and full differential tail deflections.

F-14 drop model being calibrated in flight electronics lab prior to flight tests.
Langley Contributions to the F-14

104 Grumman F-14 Tomcat

Although the drop-model results predicted that entry into the flat spin was possible, it

was recognized in this test technique that the ground-based pilot controls the model

from a remote position, thereby losing the natural physical cues available to the pilot of

the actual aircraft. In addition, the scaled model moves much faster than the full-scale

aircraft, so the time available to the pilot of the model for recovering from an impending

spin is very limited. The analysis of the F-14 therefore turned to the use of the Langley

Differential Maneuvering Simulator (DMS) where the actual human environment could

be more accurately simulated.

In 1972, a team headed by Langley researcher Luat T. Nguyen programmed the DMS

with aerodynamic data from Langley wind-tunnel test results and F-14 aircraft mass

characteristics. Arrangements were made for Langley research pilots and the Grumman

chief test pilot Charles Sewell to participate in the evaluation. Simulated maneuvers

flown in the DMS confirmed the drop-model results—that is, the aircraft could be

aggressively pitched to extreme attitudes without loss of control, but if roll control was

maintained at high angles of attack, the aircraft would depart from controlled flight. In

addition, with simulation of full-scale conditions, it appeared that the pilot had time to

make corrective controls before hazardous spin-entry conditions occurred.

Nguyen and his team had participated in the development of the flight control system for

the F-15 for high-angle-of-attack conditions. (See Langley Contributions to the F-15.)

They recognized that the concept used by the F-15 to reduce the adverse effects of the

horizontal tails as roll control devices at high angles of attack would be an ideal solution

to the F-14 problem. With this knowledge, an automatic rudder interconnect (ARI) for

the F-14 was implemented and evaluated in the DMS. The ARI system automatically

phased out movement of the tails for roll control and phased in deflections of the rudders at high angles of attack. The concept was refined and matured in the simulator studies. The pilots who flew the F-14 with the ARI system were enthusiastic, and the system

allowed the pilot to maneuver the aircraft without regard to angle of attack or switching

from differential tails to rudders. The Grumman team regarded the ARI concept developed by Langley as a highly desirable addition to the F-14 aircraft. The production contract for the early F-14 aircraft called for the implementation of an ARI system. At this

point, Langley closed out its F-14 research, while Grumman pursued the development

of the final ARI system.

Unfortunately, the early F-14 aircraft also included another late developing preproduction concept—deployable wing leading-edge maneuver slats for improved maneuverability. Early Grumman flight tests revealed that the F-14 modified with both the ARI

system and the maneuver slats displayed unsatisfactory air combat maneuvering characteristics because the ARI rudder inputs aggravated lightly damped rolling oscillations

(wing rock) induced by the slats during maneuvers. Because of this incompatibility, the

Navy deactivated the ARI systems on all fleet F-14 aircraft.

The F-14 proved to be a relatively forgiving aircraft to fly, and pilots adapted to manually switching from using differential tails for roll control at low angles of attack to

using rudders at high angles of attack. However, the F-14 fleet began to experience spin

losses at the rate of about one aircraft per year. In 1978, a joint NASA, Navy, and

Grumman program was initiated to develop a new ARI system to increase the spin resistance of the F-14. Nguyen and his team once again examined the F-14 and used the

DMS to develop a new ARI that provided adequate damping of the wing rock, while

retaining the spin resistance of the original ARI system developed by Langley. A flighttest F-14 was modified with a spin parachute, battery driven hydraulic pumps for

emergency power, and the special foldout canards on the fuselage forebody that were
Langley Contributions to the F-14

Grumman F-14 Tomcat 105

recommended by the earlier spin tunnel tests. Fitted with the new ARI, flight tests were

conducted over a 2-year period at NASA Dryden Flight Research Center with Langley

personnel on site for the flight tests. Over 100 flights by 9 pilots were made up to low

supersonic speeds.

The results of the flight-test program were extremely impressive. Wing rock was suppressed, inadvertent spins were eliminated, and the handling qualities throughout the air

combat envelope were improved. Several years passed before funding constraints permitted the Navy to develop the ARI within plans to equip the F-14 fleet with a new

advanced digital flight control system (DFCS). Following further refinements during

Navy flight evaluations at Patuxent River Naval Air Station in Maryland, the Navy

implemented the DFCS with the ARI. The first F-14 deployments with the ARI

occurred during the Kosovo operations, and glowing reports from the F-14 squadrons

indicated that the new system was a success.

The F-14 responds to an abrupt stick pull by Dryden test pilot Fitz Fulton

during evaluations of the Langley designed Automatic Rudder

Interconnect (ARI) control system at Dryden.
Langley Contributions to the F-14

106 Grumman F-14 Tomcat

Flutter Tests Flutter clearance tests of the F-14 in the Langley 16-Foot Transonic Dynamics Tunnel

required five entries from 1970 to 1973 under the leadership of Moses G. Farmer. The

utilization of variable-sweep wings by the F-14 introduced a unique flutter problem that

had been unanticipated prior to the tests. The challenge of providing an upper-fuselage

covering for the variable-sweep wing panels had been addressed by Grumman with relatively flexible inner wing covers. Early in the flutter tests, large deflections and buffeting of the over wing panels were observed and viewed as a potentially serious flutter

problem.

With knowledge of the Langley results, Grumman engineers designed a set of external

stiffening strakes for the wing covering that eliminated the flutter problem. An additional favorable impact of the strakes was local straightening of the airflow over the

upper fuselage, which resulted in performance benefits. With the strake modification,

the F-14 passed flutter clearance tests in the Langley tunnel. Initially, it was proposed

that this modification would only be applied to the preproduction flight-test F-14 aircraft

while a redesign of the wing cover could be accomplished. However the modification

proved to be extremely robust and similar strakes were incorporated in all production

F-14 aircraft.

During the flutter tests, the Langley staff observed considerable buffeting of the vertical

tails, particularly at moderate angles of attack. The staff of the 16-Foot Transonic

Dynamics Tunnel modified the cable-mount system to permit tests at high-angle-ofattack conditions where the buffeting became more intense. Langley expressed concern

that damage to the structural integrity of tails or tail-mounted avionics and antennae

might be encountered, but Grumman did not accept this concern as an issue. Subsequently, the F-14 fleet experienced structural damage and the replacement of tailmounted radar warning units. As a result, the vertical tails of F-14 aircraft were stiffened.

The experience of the engineering community with vertical-tail buffeting in the F-14 led

to the development of design analysis tools and special wind-tunnel test techniques for

follow-on aircraft including the F/A-18 and F-22.

F-14 model mounted in preparation for flutter tests

in the 16-Foot Transonic Dynamics Tunnel.

Close-up view of the external over wing cover 

strakes added to prevent panel flutter.
Langley Contributions to the F-14

Grumman F-14 Tomcat 107

F-14 Yaw Vanes In the early 1980’s, researchers in the Navy community became interested in the potential benefits of using thrust vectoring for control augmentation of the F-14. Their interest

had been spurred by a cooperative Langley and Navy piloted simulator study that was

conducted in the Langley DMS. The study defined the benefits to a representative fighter

aircraft of maintaining the control power required for satisfactory V/STOL flight in conventional flight. In this study, an existing Langley simulator model of the F-14 was modified to incorporate the control modifications under the leadership of Luat Nguyen.

Langley and DOD pilots flew the simulated flights.

Results of the simulator study showed that the most important benefit occurred when the

yaw control was augmented at high angles of attack (normally, yaw control provided by

conventional rudders is markedly reduced at high angles of attack). With the increased

yaw control capability, pilots could consistently win against a variety of adversaries in

simulated air-to-air combat. Analysis of the desired control levels in the simulator

results indicated that deflecting the engine thrust on aircraft similar to the F-14 would

provide the necessary control.

To pursue the development and demonstration of the effectiveness of yaw vectoring, the

Navy conducted a series of tests to evaluate the turning effectiveness and structural

integrity of external vanes mounted behind the nozzles of the F-14 engines. These activities were augmented by tests led by Bobby L. Berrier and David E. Reubush in the

Langley 16-Foot Transonic Tunnel. Data obtained in these tests were used to define the

geometry and thrust-vectoring effectiveness for the Navy evaluations.

Full-scale vanes were fabricated and initially ground tested behind an F-14 aircraft at

the Patuxent River facility. Flight tests of a modified F-14 were subsequently conducted

to demonstrate the structural integrity and thrust-vectoring performance of the vane concept over a limited flight envelope.

F-14 model equipped with deflectable yaw vanes in the Langley 16-Foot Transonic Tunnel.
Langley Contributions to the F-14

108 Grumman F-14 Tomcat

Further applications of the yaw vane concept to the F-14 did not develop beyond this

exploratory program, but the concept of external vanes as relatively inexpensive devices

for thrust vectoring at high angles of attack was successfully used in the NASA F-18

High-Angle-of-Attack Technology Program and the DARPA X-31 Enhanced Fighter

Maneuverability Program.

F-14 with experimental yaw vanes in flight over Patuxent River Naval Air Station.
Highlights of Research by Langley for the X-29

Grumman X-29 109

Grumman X-29

HIGHLIGHTS OF RESEARCH BY LANGLEY FOR THE X-29

1. Langley, Grumman, Defense Advanced Research Projects Agency (DARPA), and

U.S. Air Force cooperated to validate analytical methods for aeroelastic divergence

of forward-swept wings. 

2. Tests in the Langley 16-Foot Transonic Dynamics Tunnel of the X-29 resulted

in advances in design methods for aeroelastically tailored forward-swept wing

configurations.

3. Langley studied the high-angle-of-attack behavior of the X-29 and identified potential problems such as wing rock, divergent rolling motions at post-stall angles of

attack, and longitudinal tumbling motions, which permitted timely design of a robust

flight control system.

4. Critical information on engine inlet performance at high angles of attack was

obtained during tests in the Langley 14- by 22-Foot Subsonic Tunnel.

SPECIFICATIONS

Manufacturer

Grumman

First flight

December 1984

Type

Experimental demonstrator 

of advanced forward-swept 

wing and relaxed stability

Crew

One

Engine

General Electric F404-GE400

PARTICIPANTS

Grumman, DARPA, U.S. Air 

Force, and NASA

DIMENSIONS

Wingspan. . . . . . . . . . . . 27.1 ft

Length . . . . . . . . . . . . . . 53.9 ft

Height . . . . . . . . . . . . . . 14.3 ft

Wing area. . . . . . . . . 188.8 sq ft

WEIGHT

Empty . . . . . . . . . . . . 13,800 lb

Gross . . . . . . . . . . . . . 17,800 lb

PERFORMANCE

Max speed . . . . . Mach number

of 1.6
Highlights of Research by Langley for the X-29

110 Grumman X-29

The Grumman (now Northrop Grumman) X-29 demonstrated the feasibility of several

advanced technologies, including the aeroelastically tailored forward-swept wing, and

the ability to routinely operate with extremely high levels of inherent longitudinal instability (relaxed static stability). Under the Defense Advanced Research Projects Agency

(DARPA) sponsorship, Grumman designed two X-29 aircraft that underwent joint

DARPA, Grumman, NASA, and U.S. Air Force flight tests at NASA Dryden Flight

Research Center from 1984 to 1992. The exhaustive flight-test program covered aspects

such as structural and aerodynamic performance, as well as high-angle-of-attack

maneuverability. The X-29 aircraft flew 422 research missions. The joint X-29 Program

obtained a vast amount of detailed data and analysis methods that will be applied to

future high-performance aircraft.

Langley cooperated with DARPA and Grumman in the areas of flight dynamics and

engine inlet performance at high angles of attack and aeroelastic divergence of forwardswept wings. Highlights of these tests included early and accurate projections of aerodynamic, stability, and control characteristics that allowed for resolution of problems

before flight tests; rapid acceleration and validation of design methods for the avoidance

of wing divergence for forward-swept wing configurations; and risk reduction for

engine operations at high angles of attack.

Langley facilities used to support the X-29 program included the 30- by 60-Foot Tunnel,

the 20-Foot Vertical Spin Tunnel, the National Transonic Facility, the 16-Foot Transonic

Dynamics Tunnel, the 14- by 22-Foot Subsonic Tunnel, radio-controlled drop models,

and the Differential Maneuvering Simulator.
Langley Contributions to the X-29

Grumman X-29 111

LANGLEY CONTRIBUTIONS TO THE X-29

Evolution of Forward-Swept 

Wing Configurations

Research on the swept wing as a drag-reducing mechanism for high subsonic and transonic speeds during the late 1930’s and early 1940’s resulted in some of the first conventional aft-swept wing aircraft during World War II. At that time, it was also recognized

that forward-swept wings (FSW) could produce the same beneficial effect for performance. Furthermore, the FSW also promised improved low-speed controllability. Stalls

were expected to start at the wing root rather than the tip (in contrast to aft-swept

wings), thereby maintaining the effectiveness of outboard ailerons and their contributions to roll control at low speeds. The onset of shock waves at high speeds was also

expected to begin at the wing root, which again maintains aileron effectiveness at high

speeds. With lateral control effectiveness assured across the operational envelope, there

would be no need for drag-producing leading-edge high-lift devices. Finally, the general

layout of the FSW resulted in a more aft location of the wing spar carry-through structure in the fuselage, which results in more fuselage internal volume.

During 1942, the German Junkers Design Bureau initiated studies of an FSW bomber

designated the Ju-287. First flown in 1944, the Ju-287 exhibited several problems, the

most serious of which was a tendency to increase g-loading during a turn without control inputs from the pilot. The analysis of the problem by Junkers revealed that the cause

was wing structural deformation from the aerodynamic loads on the forward-facing

wingtip panels. At high speeds, the deformation was predicted to become very severe,

exceed structural limits, and result in wing failure. This potentially catastrophic phenomenon was referred to as aeroelastic divergence. Further analysis indicated that the

structural modifications required to avoid the divergence problem for the aluminum

wing of the Ju-287 would result in excessive weight and unacceptable performance penalties. Other interest in FSW configurations during World War II came from the

American Cornelius Aircraft Company, which worked on several configurations, including the XFG-1, a piloted towable glider used to transport fuel.

Researchers at Langley also investigated FSW as part of a program to develop variablesweep wings. In one of these investigations, an existing wind-tunnel model of the Bell

X-1 was equipped with a variable-sweep wing, and tests were conducted for a FSW version of the aircraft in the Langley 300-MPH 7- by 10-Foot Tunnel.

Following World War II, the only significant FSW aircraft built was the German

Hansajet business jet, which was designed by the same chief engineer who designed the

Ju-287. The aircraft never enjoyed a large market.

The German Junkers Ju-287 forward-swept-wing bomber.
Langley Contributions to the X-29

112 Grumman X-29

The problem of aeroelastic divergence stood squarely in the progress of FSW options

for relatively high-speed aircraft, and the challenge of providing sufficient rigidity versus weight turned many designers away from the concept.

In the 1970’s, two activities coupled to stimulate interest in FSW configurations. First,

Grumman became interested in conducting aerodynamic research to determine methods

to improve its Highly Maneuverable Aircraft Technology (HiMAT) configuration,

(which had lost in the design competition to Rockwell) including revolutionary wing

configurations. The second activity was the remarkable advocacy and influence of

Dr. Norris J. Krone, Jr., a retired Air Force pilot who had written his doctoral thesis on

eliminating aeroelastic divergence of FSW configurations by using advanced tailored

composites for structural rigidity. Krone subsequently became a manager at the Defense

Advanced Research Projects Agency (DARPA), and Krone’s discussions with the

Grumman managers led to a resurgence of interest in an examination of the FSW concept. During 1977, DARPA released a request for proposals (RFP) for a highly

advanced technology demonstrator that would integrate advanced aerodynamics (with

emphasis on the FSW) and advanced flight controls. Responses were received from

Grumman, Rockwell, and General Dynamics.

On December 22, 1981, DARPA announced that Grumman had been selected to

develop the new technology demonstrator, to be known as the X-29.

High-Angle-of-Attack 

Technology

Initial information exchanges between DARPA and Langley on independent high-angleof-attack evaluations of the competing FSW configurations occurred in early 1980,

when Krone visited Joseph R. Chambers and his staff at the 30- by 60-Foot (Full-Scale)

Tunnel. Langley agreed to provide support in this area as requested for all three competing industry teams. General Dynamics proposed an FSW version of the F-16 as a candidate design for the DARPA competition. Exploratory static wind-tunnel data had

already been generated by cooperative tests led by Langley researcher Sue B. Grafton in

the Langley 12-Foot Low-Speed Tunnel in 1978. Final tests of the General Dynamics

design occurred in the Full-Scale Tunnel in April 1980. Rockwell’s FSW configuration

underwent preliminary static and dynamic tests in the Full-Scale Tunnel in March 1981.

Grumman’s FSW configuration was tested in the same tunnel during three entries beginning in November 1980. As a result of these tests, DARPA was provided with a timely,

independent assessment of the high-angle-of-attack characteristics of all three competing designs. Langley gained considerable experience with the unique aerodynamic, stability, and control characteristics of FSW configurations at high angles of attack.

Following the award of DARPA’s X-29 contract to Grumman, Langley’s support in the

area of high-angle-of-attack technology expanded to include additional dynamic force

tests and free-flight model tests in the Full-Scale Tunnel, spin and spin recovery tests in

the Langley 20-Foot Vertical Spin Tunnel, control system development studies and

piloted assessments of high-angle-of-attack behavior in the Langley Differential

Maneuvering Simulator (DMS), and assessments of spin-entry and post-stall motions

using a radio-controlled drop model.

One of the most important, unexpected results of the X-29 high-angle-of-attack study

came during preliminary static and dynamic tests of a 0.16-scale free-flight model in the

Full-Scale Tunnel. The X-29 government and industry team (and the entire technical

community) had expected the X-29 to be heavily damped in roll at high angles of attack

as a result of the tendency of the FSW to maintain attached airflow at the wingtips

during stall. However, when Sue Grafton conducted the first dynamic force tests to
Langley Contributions to the X-29

Grumman X-29 113

measure aerodynamic damping in roll, the results indicated that the X-29 configuration

would exhibit very unstable values of roll damping at angles of attack above about

25 deg. This result came as a complete surprise, and additional tests were quickly

planned to confirm the suspected impact of the unstable damping. Grafton conducted a

special “free-to-roll” test, in which the X-29 model was mounted to a sting assembly

that contained a roll bearing which provided a 360-deg roll capability. The test technique evaluated the tendency of the model to display unsatisfactory roll characteristics

at high angles of attack. At low angles of attack, the model was very stable, with no tendency to oscillate or diverge (in agreement with the results of the dynamic force test).

When the angle of attack of the model was increased to about 25 deg, however, the

model suddenly exhibited large amplitude wing rocking motions of a periodic nature.

The wing rock was a nonlinear phenomenon, in that the model motions were selfinitiating and built up to a limited amplitude independent of the magnitude of the initial

disturbance.

The early identification of the wing rock led to more tests, wherein it was determined

that the wings of the X-29 were indeed working as predicted. That is, the airflow

remained attached at the wingtips. However, vortical flow shed from the long, pointed

forebody of the X-29 was found to be interacting on the upper fuselage and inner wing

and causing the unstable damping, which was so large that it overwhelmed the stabilizing influence of the attached flow at the wingtips. Interestingly, the X-29 incorporated

Sue Grafton with the F-16 forward-swept-wing model.
Langley Contributions to the X-29

114 Grumman X-29

the forward fuselage of the Northrop F-5A, which is also known to exhibit wing rock at

low speeds and high angles of attack because of the same phenomenon. With the cause

of the instability identified, the X-29 flight control system could be modified to increase

the level of the artificial roll damping provided by feedback to the flaperons. Fortunately, the flaperons of the X-29 retained their effectiveness because of the favorable

flow patterns of the FSW at high angles of attack. Estimates indicated that sufficient

damping could be provided by the flight control system via the roll damper, which utilized the flaperons.

Free-flight tests of the X-29 model were first conducted in the Full-Scale Tunnel in

January 1982. A special challenge faced the Langley team, since the X-29 airframe was

designed for a very high level of aerodynamic instability in pitch (relaxed static stability) with a highly responsive, redundant flight control system that provided stability

augmentation. The X-29 would be unflyable without the stabilizing inputs of the stability augmentation system. No other aircraft (and no other free-flight model) had ever

flown with such a high level of relaxed stability. The X-29 incorporated a level of

relaxed longitudinal stability (-32 percent at low speeds) that was an order of magnitude

more unstable than the F-16. Under the leadership of Luat T. Nguyen, the staff programmed the X-29 control laws into the Langley computer that was used to replicate

full-scale controls for the model flight tests. With a vane on the model nose boom providing information on angle of attack, the control system of the model performed

flawlessly during the entire test program. The X-29 model became the first flying vehicle with such a level of relaxed stability.

X-29 free-flight model undergoing tests at high angles of attack in the Langley Full-Scale Tunnel.
Langley Contributions to the X-29

Grumman X-29 115

During the free-flight tests led by Daniel G. Murri and Sue Grafton, the model exhibited

large amplitude wing rock near an angle of attack of 25 deg when the roll damper component of the flight control system was turned off, as had been observed in the free-toroll tests. The wing rock became more severe with increasing angle of attack, and flights

usually resulted in loss of control of the model near an angle of attack of 30 deg. The

amplitude and frequency of the motions were in close agreement with the preliminary

tests. When the roll damper was engaged, the motions quickly damped out and the

model displayed satisfactory characteristics.

The timely identification of the unstable roll damping of the X-29 configuration was a

major contribution of Langley for the aircraft. If the full-scale aircraft flight program

had begun without the provision for adequate control system gains and an awareness of

a possible roll-damping problem, the high-angle-of-attack characteristics of the X-29

could have been unacceptable. Ultimately, the X-29 did display the wing rock tendency

in flight (although not to the degree of severity indicated by the model tests). However,

the controls of the full-scale aircraft were even more effective than those of the freeflight model, and the control system had been designed with provision to increase the

gain of the roll damper. The two X-29 aircraft subsequently exhibited entirely satisfactory characteristics in flight, and the technical community learned a lesson regarding

the integrated aerodynamic contributions of FSW configurations with long, pointed

fuselages.

In 1983, Luat Nguyen led a piloted assessment of the X-29 at high angles of attack in

the DMS. The objectives were to study the high-angle-of-attack flying characteristics of

the aircraft and its susceptibility to departure under maneuvering conditions, identify

and develop control law concepts to provide good flying qualities and a high level of

departure-spin resistance, assess the effectiveness of the Grumman flight control laws at

high angles of attack and provide recommendations for modifications, and provide support for flight-test planning and coordination with NASA Dryden Flight Research

Center.

A priority issue in the DMS studies was the effect of Reynolds number on aerodynamic

characteristics. Results of high Reynolds number tests in the NASA Ames 12-Foot Pressure Tunnel indicated that significant effects of Reynolds number on pitching moments

and yawing moments existed for the X-29 configuration. Working with flight control

team members from Grumman and Dryden, Nguyen completed an in-depth study of

X-29 handling qualities at high angles of attack and provided numerous recommendations for the specific design of the flight control system for high-angle-of-attack conditions. Control law concepts were identified for control surface interconnects for

optimum roll coordination, wing rock suppression, and automatic departure and spin

prevention.

Spin Tunnel Tests Tests of the X-29 in the Langley 20-Foot Vertical Spin Tunnel, which began in 1981

under Raymond D. Whipple, concentrated on three areas. First, the developed spin and

spin recovery characteristics of the X-29 were determined for various aircraft loadings

and erect and inverted spins. As previously mentioned, large Reynolds number effects

had been predicted for the X-29 configuration. These effects were very noticeable at

very high angles of attack (near 90 deg), where the model might exhibit critical spins.

To correct for these effects (which were caused by the unique forebody shape that was

incorporated from the F-5A) at the low speeds involved in the Spin Tunnel conditions,

the Langley staff employed auxiliary strakes on the nose of the X-29 spin model. The
Langley Contributions to the X-29

116 Grumman X-29

X-29 model exhibited two types of spin. One type was flat, with an angle of attack of

about 85 deg, with marginal to unsatisfactory spin recovery. The second spin was very

oscillatory, with satisfactory to excellent recovery characteristics.

The second area of interest was determination of the size of the emergency spin recovery parachute required for the number 2 aircraft, which would be used in the high-angleof-attack flight-test program. Working with Grumman and Dryden, Whipple and the

X-29 team arrived at a recommended parachute size, truss structure, and deployment

mechanism. As a result of the outstanding maneuverability and spin resistance exhibited

by the X-29, the emergency parachute system was never utilized in flight tests to terminate post-stall maneuvers.

The third area of interest in the Spin Tunnel test program involved concern over the possibility of a longitudinal tumbling phenomenon for the X-29. This concern had risen

because of the high level of inherent longitudinal instability designed into the X-29.

Specifically, Langley researchers expressed concern over whether the combination of

very low airspeed and very high angle of attack (such as during recovery from a “zoom

climb” to zero airspeed) might result in the aircraft pitching over into an end-over-end

tumbling that would result in incapacitating g-levels for the pilot. The Spin Tunnel staff

first addressed this issue in free-spinning tests wherein the X-29 model was launched

tail first, without rotation, into the vertically rising airstream. The results of these

exploratory tests showed that, without inputs from the control system, the model would

indeed pitch over and develop a continuous tumbling motion about its center of gravity.

The wild gyrations quickly caused the spin tunnel model to impact the walls of the tunnel, so an additional test technique was developed to study the issue under more controlled conditions. In these tests, the model was mounted on a special single-degree-offreedom test apparatus that permitted 360-deg free-pitching motions. The additional

The spin parachute and truss assembly on the X-29 during high-angle-of-attack tests at Dryden.
Langley Contributions to the X-29

Grumman X-29 117

studies of tumbling on this apparatus provided insight to a possible solution to the problem. The X-29 flight control system included aft-fuselage strake flaps, which were

intended to be used only as trimming devices. However, during the tumbling tests it was

found that the strake flaps were extremely efficient in promoting recovery from the tumble motions. In view of this result, the control system was modified to permit use of the

strake flaps as control devices. This approach prevented the X-29 from entering the

uncontrollable tumbling motions.

Drop-Model Tests In 1987, Langley upgraded its drop-model test technique and conducted studies of the

high-angle-of-attack and post-stall characteristics of a 0.22-scale model of the X-29.

The high degree of relaxed stability of the X-29 made high-fidelity simulation of the

control system a mandatory feature of the drop model. Langley had never flown an

unstable model before the X-29 program. The Langley staff, led by Mark A. Croom,

upgraded nearly every element of the drop-model operation, such as the model control

actuators, transmitters and receivers, data encoders and decoders, and operational displays including a new cockpit display and operations monitor. The advanced X-29 control laws developed in the DMS study were programmed into a ground-based computer

for proper simulation of control effects. This activity was by far the most challenging

drop-model project ever conducted by Langley to that time.

X-29 model mounted on single-degree-of-freedom

pitch-tumble test apparatus in the Langley Spin Tunnel.
Langley Contributions to the X-29

118 Grumman X-29

The results of the drop-model program further confirmed the need for special control

system concepts for high-angle-of-attack conditions. Without artificial stability augmentation in roll, the drop model exhibited the same type of large amplitude wing rock

motions previously displayed by the wind-tunnel free-flight model. In the case of the

drop model, when the angle of attack was increased to 30 deg and beyond, the oscillations became so divergent that the model exhibited uncontrollable 360-deg rolls that

evolved into a roll departure and post-stall gyrations. When the wing rock suppression

system was engaged, the motions were damped and the model was controllable to very

high angles of attack.

During some flights at extreme angles of attack, asymmetric yawing moments were

encountered that caused the model to yaw and generate relatively high rotational rates.

When the pilot intentionally applied prospin control inputs during these conditions, the

model sometimes entered the unrecoverable flat spin mode exhibited by the spin tunnel

model. With the departure and spin prevention system engaged, the model was highly

resistant to intentional spins and was extremely maneuverable at high angles of attack.

Another valuable contribution of the X-29 drop-model program was a parameter identification effort conducted by David L. Raney and James G. Batterson of Langley, in

which they analyzed the wing rock motions of the drop model and extracted values of

the critical aerodynamic parameters that caused the motions. This complex analysis

required the identification of rapidly changing aerodynamic derivatives over a range of

angle of attack. The results of the study clearly identified unstable values of aerodynamic damping in roll to be the cause of the wing rock motions.

X-29 drop model mounted on launch apparatus on side

of helicopter prior to release for post-stall tests.
Langley Contributions to the X-29

Grumman X-29 119

Engine Inlet Tests Grumman requested support from Langley in assessing the static and dynamic pressure

conditions that might be experienced by the engine inlets during the high-angle-ofattack flight tests of the X-29. The data were required to ensure satisfactory engine operation and avoid engine stalls that could result in loss of hydraulic power during the spin

maneuvers. Langley responded with tests of a powered X-29 model in the 14- by

22-Foot Subsonic Tunnel. The model was equipped with a propulsion simulator, flowthrough inlets, and extensive instrumentation. These tests occurred in 1991 under the

leadership of John W. Paulson, Jr.

Aeroelastic Divergence The phenomenon of aeroelastic divergence had dramatically constrained international

interest in the application of conventional metal FSW concepts. Franklin W. Diederich

and Bernard Budiansky of Langley studied and summarized the major challenges of the

divergence phenomenon in a NACA Technical Note in 1948 (ref.1). However, the emergence of composite materials and the aggressive advocacy of Norris Krone to utilize

aeroelastic tailoring to reduce divergence led to cooperative studies of FSW technology

by the staff of the Langley 16-Foot Transonic Dynamics Tunnel (TDT). Rodney H.

Ricketts, Robert V. Doggett, and Wilmer H. Reed, Jr. planned and participated in numerous studies with DARPA, the Air Force, and industry to develop and verify analytical

predictions of the divergence phenomenon. The studies investigated systematic generic

wings and specific configurations, including the Rockwell and Grumman FSW designs.

X-29 powered-inlet model tests in the

Langley 14- by 22-Foot Subsonic Tunnel.
Langley Contributions to the X-29

120 Grumman X-29

The analyses and tests of generic wing models with variations in aspect ratio, airfoils,

and sweep provided invaluable data and methods that significantly expanded the database, especially in the transonic regime. Six subcritical response test techniques were

formulated and evaluated at transonic speeds for accuracy in predicting static divergence, and two divergence stoppers were developed and evaluated for use in preventing

structural damage of wind-tunnel models during divergence tests.

Ricketts led cooperative tests of the proposed Grumman and Rockwell FSW configurations in the TDT in 1979. NASA, DARPA, the U.S. Air Force, and the industry teams

participated in the cooperative tests. The Rockwell model consisted of a semispan wing

mounted to a splitter plate on the tunnel sidewall. The Grumman model included a

representative fuselage shape. Conclusions from the divergence tests included dramatic

demonstrations that aeroelastic tailoring was extremely effective in suppressing divergence for FSW configurations and that new nonlinear aerodynamic theories were

required for complete analysis of the phenomenon. After the DARPA X-29 contract was

awarded to Grumman, additional tests were conducted in the TDT in 1983 which demonstrated the potential coupling of the wing structural modes with the rigid body pitch

mode to create an instability called body-freedom flutter. Techniques were developed to

analyze these wing-body interactions, and the wing divergence prediction methods

developed at Langley were used in the flight-test program of the X-29 at Dryden.

Advanced Engine Nozzle In the early 1970’s, an advanced thrust-vectoring nozzle for V/STOL aircraft was

designed by the General Electric Company under a contract funded by the Navy. The

nozzle was designed with a deflectable internal hood to permit large pitch thrust-vector

angles for V/STOL operations, while deflection of the single expansion ramp could be

used for smaller thrust-vector angles during air-to-air combat. This nozzle, known as the

augmented deflector exhaust nozzle (ADEN), received considerable test and developmental support in the technical community during the 1970’s and early 1980’s. Much of

this activity was advocated by the Department of Defense (DOD), NASA, the U.S. Air

Rodney Ricketts with the Grumman FSW model during aeroelastic

divergence tests in the Langley 16-Foot Transonic Dynamics Tunnel.
Langley Contributions to the X-29

Grumman X-29 121

Force, and the U.S. Navy ad hoc interagency nonaxisymmetric nozzle working group

that included Langley researcher Bobby L. Berrier as the NASA representative. The

Propulsion Aerodynamics Branch at Langley conducted much of the development work

on the ADEN under the direction of William P. Henderson and Bobby Berrier. Numerous cooperative ADEN research programs with DOD and industry were conducted to

optimize nozzle performance and define suitable propulsion-airframe integration methodologies on a series of generic and specific (e.g., F-18) fighter configurations. The first

full-scale nonaxisymmetric nozzle test was conduced at the Glenn Research Center in

1976 by running an ADEN nozzle attached to an augmented General Electric YJ101

engine in an altitude test cell. Thus, by the time of the DARPA X-29 award to Grumman

in 1981, a mature thrust-vectoring nozzle design was available.

During the early phases of the X-29 program, NASA Headquarters expressed interest in

the application of the ADEN to the canard configured X-29 as an exploratory flight-test

bed, since the canard of the X-29 could counterbalance the effects of the deflected

ADEN nozzle. The NASA interest in the X-29 ADEN was to promote technical

progress in vectorable nozzles and ensure that a sufficient number of candidate nozzles

were considered for further development.

Simple ADEN-like nozzle configuration (pitch and yaw vectoring)

flown on X-29 free-flight model in the Full-Scale Tunnel.
Langley Contributions to the X-29

122 Grumman X-29

NASA Headquarters requested Langley’s assessment of the X-29 ADEN configuration

for further advocacy discussions with Grumman and DARPA. Although no induced lift

or aerodynamic wing lift augmentation would occur for this configuration, the addition

of vectoring was believed by Langley to improve high-angle-of-attack controllability. In

response to this request from Headquarters, Joseph L. Johnson, Jr. and his staff at the

Full-Scale Tunnel quickly modified their X-29 free-flight model and conducted exploratory evaluations of the handling qualities of the X-29 ADEN at high angles of attack in

1984. During these tests, a yaw-vectoring side-door capability (a concept defined and

tested by the Propulsion Aerodynamics Branch in the Langley Jet Exit Test Facility) was

added to a simplified ADEN-type nozzle to provide both pitch and yaw vectoring, and

the resulting flight tests demonstrated a dramatic improvement in controllability and

agility of the X-29 at extreme angles of attack. The model could be flown with precise

and effective control to angles of attack as high as 85 deg. These positive results were

typical of those that had been obtained with several different aircraft configurations

equipped with other thrust-vectoring nozzles. The national progress in nonaxisymmetric, thrust-vectoring nozzles led to interest in other nozzle configurations and the eventual successful F-15 short takeoff and landing and maneuver technology demonstrator

(STOL/MTD), F-18 High Alpha Research Vehicle (HARV), and X-31 flight-test

programs.

X-29 ADEN model flying at an angle of attack of 80 deg in the Langley Full-Scale Tunnel.
Highlights of Research by Langley for the C-5

Lockheed C-5 Galaxy 123

Lockheed C-5 Galaxy

HIGHLIGHTS OF RESEARCH BY LANGLEY FOR THE C-5

1. The aerodynamic performance of three competing industry configurations for the

C-5 contract was determined by model tests in the Langley 8-Foot Transonic Tunnel.

2. Aerodynamic interference between the wing and the large engine nacelles and

pylons were measured during tests in the 8-Foot Transonic Tunnel.

3. Parametric tests in the Langley 16-Foot Transonic Dynamics Tunnel of a clippedspan C-5 model identified an abrupt drop in tail flutter speed at transonic Mach numbers that required increased stiffening of the fin spar.

4. An active load alleviation system was developed in the Langley 16-Foot Transonic

Dynamics Tunnel.

5. Powered-model tests in the Langley 30- by 60-Foot (Full-Scale) Tunnel provided

information on C-5 airdrop (wake) characteristics and power effects for the landing

configuration.

6. Tests of a C-5 model were conducted to determine an optimum ditching configuration.

SPECIFICATIONS

Manufacturer

Lockheed

Date in service

C-5A. . . . . . . December 1969

C-5B . . . . . . . . . January 1986

Type

Transport

Crew

Six

Engine

General Electric TF39-GE-1C

USERS

U.S. Air Force (Active, Air 

National Guard, and Reserve)

DIMENSIONS

Wingspan. . . . . . . . . . . 222.8 ft

Length . . . . . . . . . . . . . 247.8 ft

Height . . . . . . . . . . . . . . 65.1 ft

Wing area. . . . . . . . . 6,200 sq ft

WEIGHT

Empty . . . . . . . . . . . 370,000 lb

Max takeoff . . . . . . . 837,000 lb

PERFORMANCE

Cruise speed . . . . . . . 563 mph

Range. . . . . . . . . . . . 3,000 n mi
Highlights of Research by Langley for the C-5

124 Lockheed C-5 Galaxy

The Lockheed (now Lockheed Martin) C-5 Galaxy heavy-cargo transport provides strategic airlift for the worldwide deployment and supply of combat and support forces. The

C-5 can carry unusually large and heavy cargo for intercontinental ranges at high subsonic speeds. The aircraft can take off and land in relatively short distances and taxi on

substandard surfaces during emergency operations. The C-5 is one of the largest aircraft

in the world. It is almost as long as a football field and is as tall as a 6-story building

with a cargo compartment about the size of an 8-lane bowling alley. The C-5 and the

smaller C-141B Starlifter are strategic airlift partners. Together they can carry fully

equipped, combat ready troops to any area in the world on short notice and provide the

full field support necessary to maintain a fighting force. The C-5 can carry a payload

that is more than twice as heavy as the C-141 payload. The lower deck of the C-5 has an

unobstructed length of 121 ft and width of 19 ft that enables it to carry any piece of

Army equipment, including self-propelled howitzers, personnel carriers, and tanks—

none of which can enter the payload bay of the C-141.

Langley’s contributions to the C-5 program included wind-tunnel tests and performance

analysis of the competing industry designs during the Cargo Experimental–Heavy

Logistics System (CX–HLS) Program that resulted in the C-5. Langley conducted windtunnel assessments of engine and wing aerodynamic interactions; flutter studies of the

T-tail configuration; flutter clearance tests for the complete configuration; wind-tunnel

studies of an active load alleviation concept; flow surveys behind the configuration for

analysis of airdrop characteristics; assessments of power-induced effects in the landing

configuration, including studies of potential applications of the externally blown flap

concept (subsequently incorporated in the C-17 transport); and model tests to determine

the optimum ditching configuration. Langley facilities involved in C-5 tests included the

8-Foot Transonic Tunnel, the 16-Foot Transonic Dynamics Tunnel (TDT), the 16-Foot

Transonic Tunnel, the 30- by 60-Foot (Full-Scale) Tunnel, and the Langley Impacting

Structures Facility (Tow Tank).
Langley Contributions to the C-5

Lockheed C-5 Galaxy 125

LANGLEY CONTRIBUTIONS TO THE C-5

C-5 Evaluation In 1964, the Air Force awarded study contracts to Boeing, Douglas, and Lockheed for

the design of a heavy-lift transport for the Cargo Experimental–Heavy Logistics System

(CX–HLS). In December 1964, the three manufacturers were invited to submit proposals for the new transport, which was intended to carry bulky and heavy military equipment that could not be accommodated in the C-141. All three industry designs

incorporated high-wing configurations with four large turbofan engines in underwing

nacelles and front and rear doors with ramps for flow-through loading and unloading.

The Boeing and Douglas designs had conventional tail configurations, whereas the

Lockheed design incorporated a T-tail configuration.

At the request of the Department of Defense (DOD), Langley conducted aerodynamic

assessments of all three designs in the Langley 8-Foot Transonic Pressure Tunnel in

1965 under the leadership of Langley researcher Dr. Richard T. Whitcomb. The results

of these tests were provided to a committee to select the winning C-5 design. In an

extremely controversial decision based on proposal cost estimates, industry workloads,

and geopolitical considerations, the Air Force announced in October 1965 that

Lockheed had been selected to proceed with development of their C-5 design.

The C-5 design submitted by Boeing was found to have superior aerodynamic cruise

performance in the transonic wind-tunnel tests performed at Langley. Boeing’s experience with the C-5 competition coupled with Boeing management’s vision of the marketability of jumbo civil transports (and interest from Pan American Airlines) led to the

development of the Boeing 747, which enabled Boeing to dominate the world market

with a new product line. Although the 747 was a completely new aircraft design (low

wing, passenger-carrying civil aircraft), the general configuration influence of the earlier

C-5 candidate is in evidence.

Research on Sting Interference 

Effects

Analysis of the data from the Langley 8-Foot Transonic Pressure Tunnel tests of the

three C-5 configurations indicated that the high degree of aft-fuselage bottom upsweep

of all the configurations increased cruise drag (especially the Douglas design, which

had 19 deg of upsweep). Because of the critical nature of the aft-end drag, concern

arose over potential interference effects caused by the model support sting on drag

measurements.

Donald L. Loving and Arvo A. Luoma conducted tests in 1965 of all three configurations with conventional stings, dummy stings, and dorsal strut-support systems over a

limited range of test variables from just below to just above the design cruise condition

of each configuration. The results of their investigation indicated that the sting interference effects were of very small magnitude.

Research on Effects of Test 

Section Size

Also in 1965, a study was conducted by Langley researchers Arvo Luoma, Richard J.

Re, and Donald Loving to address concerns over the effect of model size during transonic tests of large models in the 8-Foot Transonic Pressure Tunnel. In wind-tunnel

tests, the largest model possible is generally desirable so that higher model Reynolds

numbers are obtained, but if the model is too large potential tunnel wall effects and data

corrections become concerns, especially at high subsonic and transonic speeds. Comparative aerodynamic data were obtained for the same 5-ft-span model of the C-5 in the
Langley Contributions to the C-5

126 Lockheed C-5 Galaxy

Competing C-5 configurations during tests in the Langley 8-Foot Transonic

Pressure Tunnel. Top to bottom: Douglas, Lockheed, and Boeing designs.
Langley Contributions to the C-5

Lockheed C-5 Galaxy 127

Langley 8-Foot Transonic Pressure Tunnel and the Langley 16-Foot Transonic Tunnel

for Mach numbers from 0.75 to 0.83. The 5-ft-span model was two to three times larger

than usual models tested in the Langley 8-Foot Transonic Pressure Tunnel.

The results of the study indicated that the data obtained in the two tunnels were in good

agreement and that large models could be tested in a slotted tunnel such as the 8-Foot

Transonic Pressure Tunnel at subsonic speeds with acceptable results.

Propulsion Integration 

Research

In 1966, Langley researchers James C. Patterson, Jr. and Stuart G. Flechner conducted

parametric studies in the Langley 8-Foot Transonic Pressure Tunnel to determine the

effects of large high-bypass engines on the interference drag of wing-nacelle configurations at cruise conditions. In the study, a large powered semispan model that incorporated tip-driven, nitrogen-powered engine simulators was used. The baseline model

configuration represented the C-5; however, the horizontal and vertical positions of the

engines relative to the wing were varied so the effects of the engine exhaust wakes could

be studied in detail. The results of the study indicated that the interference drag

effects could actually be beneficial for certain combinations of wing-nacelle geometric

parameters.

C-5 model mounted for tunnel test section study in the Langley 16-Foot Transonic Tunnel.

Powered C-5 semispan model in the Langley 8-Foot Transonic Pressure Tunnel.
Langley Contributions to the C-5

128 Lockheed C-5 Galaxy

Low-Speed and Wake 

Characteristics

In late 1965, the Air Force requested that tests be conducted in the Langley 30- by

60-Foot (Full-Scale) Tunnel to investigate the application of the externally blown flap to

the C-5 aircraft. Close examination of the C-5 configuration indicated that the engine

exhaust would blow strongly on the trailing-edge flaps and that the aircraft would probably have considerable jet-flap lift effect in its basic configuration. The jet-flap lift effect

might be sufficient to promote marked improvements in takeoff and landing performance that had not been anticipated. However, the jet-flap effect could induce pitch and

roll trim problems that were also not anticipated. The Air Force request included tests of

a semispan powered model, as well as a full-span powered model.

The examination by Langley of the C-5 configuration indicated that several features of

the wing and flap did not lend themselves well to adaptation of a high efficiency jet-flap

arrangement. For example, the flap configuration was not optimum for blown flap applications. As a result of concern expressed by Langley, a two phase program was conducted. The first phase of the program measured the effects of power on lift and drag

characteristics and the effect of power (and engine-out conditions) on the longitudinal

and lateral trim requirements, control, and stability of the basic C-5 configuration. The

second phase of the research program consisted of modifying the wing and flap system

to provide a more optimal configuration for an efficient jet flap.

In 1966, a powered semispan model of the C-5 underwent two test entries in the FullScale Tunnel to determine a limited amount of power effects, including the effects of

thrust reversers. Unfortunately, Lockheed changed the trailing-edge flap system of the

C-5 from a double-slotted configuration to a Fowler flap configuration, and the tests had

to be conducted with an outdated flap system.

In 1967, a full-span 0.057-scale model of the C-5 was tested in the Full-Scale Tunnel to

determine the effect of the externally blown flap concept on the aircraft. The initial work

was done with the original, nonoptimized double-slotted flap design. Subsequent work

was done with a new flap system that was designed specifically for the blown flap concept by the Langley staff under the leadership of Joseph L. Johnson, Jr.

Powered C-5 model mounted in the Langley Full-Scale Tunnel

for externally blown flap assessments with the

double-slotted flap configuration.
Langley Contributions to the C-5

Lockheed C-5 Galaxy 129

The results of the wind-tunnel study indicated that, as had been predicted by Langley,

the blown flap effectiveness for the original double-slotted flap configuration was relatively modest. Modifications required to obtain a more optimal externally blown flap

configuration were fairly extensive, including new trailing-edge flaps, relocation of the

horizontal tail, and resizing of the vertical tail and rudder for control of engine-out conditions. Although such modifications were beyond the scope and interests of the C-5

program, Langley conducted additional wind-tunnel tests of the modified C-5 configuration, including free-flight model tests and piloted simulator studies. Although not

applied to the C-5, this research provided critical information, design guidelines, and

solutions to engine-out issues that were extremely helpful in the risk reduction and ultimate development of the C-17 transport.

At the request of the Army, a survey of the flow in the wake of the C-5 full-span model

was made in early 1968 in the Full-Scale Tunnel to define the dynamic pressure and

flow angularity for analyses of the airdrop capability of the C-5.

Tail Flutter The staff of the Langley 16-Foot Transonic Dynamics Tunnel (TDT) led research on

flutter characteristics of the T-tail configuration as a design feature of large transport aircraft with transonic cruise capabilities in the late 1950’s. Although several aerodynamic

theories had been developed for predicting subsonic and supersonic flutter of T-tails, the

transonic regime posed special challenges because transonic flutter speeds tend to be

lowest and are accompanied by complex shock patterns that make flutter analyses difficult. TDT staff members Charles L. Ruhlin and Maynard C. Sandford had been actively

involved in the flutter issues that faced the C-141 and had contributed to the databases

for the design of flutter-free T-tails for future aircraft. Their pioneering efforts in the

C-141 program resulted in new test procedures, validation of computational methods,

and fundamental research of the complex aerodynamic and structural coupling for the

new tail designs. Two types of T-tail flutter had been identified by research: symmetric

tail flutter, which was dominated by pitching-type relative motions of the surfaces, and

antisymmetric flutter, which was characterized by yawing and rolling relative motions

of the tail surfaces. Antisymmetric flutter is especially complex, and more data were

needed to advance the understanding and design tools.

Langley engineer Charles C. Smith, Jr. conducts flow

visualization studies on the modified C-5 model.
Langley Contributions to the C-5

130 Lockheed C-5 Galaxy

Ruhlin and Sandford developed an innovative approach to testing large, isolated-tail and

aft-fuselage models, which permitted more accurate simulation of structural and aerodynamic properties of full-scale aircraft. In late summer of 1966, they began studies of an

isolated 1/13-scale model of the C-5 empennage, fuselage, and inner wings in the TDT.

The T-tail, fuselage, and inboard wings were geometrically, dynamically, and elastically

scaled. Two models of the T-tail were tested—one was built with the C-5 design stiffness, while the second had only half the design stiffness.

The tail flutter speeds for the designed C-5 empennage were beyond the required flutter

demonstration speeds; however, a pronounced decrease in flutter speed was observed

slightly above the maximum Mach number (between 0.92 and 0.98). As a result of these

tests, the fin spar stiffness was increased, and flutter clearance for the full-span C-5

model in the TDT was subsequently obtained.

Clipped wing model of the C-5 in the Langley 16-Foot Transonic Tunnel for flutter tests.

Full-span model of the C-5 in the Langley 16-Foot Transonic Dynamics Tunnel.
Langley Contributions to the C-5

Lockheed C-5 Galaxy 131

Load Alleviation In the initial design of the C-5, Lockheed implemented an aggressive weight reduction

program to meet performance requirements. The wing weight was reduced by using

higher design stress levels and reducing primary component thickness. The higher stress

levels proved to be a problem, and wing cracks were found early in full-scale ground

fatigue tests in July 1969. After the aircraft had been in service several years, a wing

tear-down inspection on one aircraft with a high number of flight hours revealed significant cracks. Lockheed proposed several approaches to restore C-5 wing fatigue life to a

specified level of 30,000 flying hours. These approaches included (1) an active aileron

system to alleviate gust loads on the wing, (2) local wing modifications to improve

fatigue, and (3) redistribution of fuel within the wing to reduce bending moments.

Langley researchers Ruhlin and Sandford conducted tests of the C-5 active lift distribution control system (ALDCS) in the 16-Foot Transonic Dynamics Tunnel in 1973. The

results of this study validated the use of active control technology for the minimization

of aircraft aeroelastic response and showed that scaled aeroelastic wind tunnel models

can be used in developing active control systems.

Active ailerons were retrofitted to 77 C-5’s in 1975 through1977. That approach, however, was superseded by a redesign of the wing that included a new center wing, two

inner wing boxes, and two outer wing box sections, which were manufactured from

advanced aluminum alloys that were unavailable when the original wings were produced in the late 1960’s and early 1970’s. As a result, all C-5 aircraft were modified with

the new wings.

Ditching Tests Langley conducted ditching investigations for military and civil aircraft (including the

Space Shuttle) for many years in a water tank facility known as the Langley Impacting

Structures Facility. Following World War II, aircraft shapes and sizes did not vary significantly from the existing database that was generated by the Langley research. However, the introduction of the C-5 and other large wide-body civil transports required the

prediction of ditching characteristics for heavier and larger configurations that were not

Active load alleviation test of the C-5 in the

Langley 16-Foot Transonic Dynamics Tunnel.
Langley Contributions to the C-5

132 Lockheed C-5 Galaxy

C-5 model in Langley Impacting Structures Facility for ditching tests.

C-5 ditching model with simulated structural skin on bottom of model.
Langley Contributions to the C-5

Lockheed C-5 Galaxy 133

included in the database. The design configuration and structural features of large cargo

and transport aircraft also required that a dynamic model be investigated to determine

overall motions, accelerations, and the approximate location and amount of damage that

might be expected during a ditching at sea. In addition, the large number of main landing gear wheels (24) for the C-5 and the ability of the landing gear to be extended to various positions offered the possibility of an optimal ditching configuration, since

previous wheels-down dynamic-model investigations had shown a wide variation of

ditching performance with landing gear extended.

At the request of the Air Force, Langley researcher William C. Thompson conducted

ditching studies of a 1/30-scale model of the C-5 in the Impacting Structures Facility in

1969. The model was highly instrumented to measure accelerations, and a special

scaled-structure lower fuselage was included to determine the structural damage

incurred in ditching. The tests included various impact attitudes, flaps up and down, and

landing gear retracted and down in simulated calm and rough (simulated sea state 4)

water. Results of the study indicated that the most favorable condition for ditching was a

7-deg nose-high attitude with the flaps down 40 deg, the nose gear retracted, and the

main gear fully extended. For these conditions, damage to the fuselage bottom would

occur, and most of the main landing gear would probably be torn away.

Wind-Tunnel Test to FlightTest CorrelationAnalysis of flight data obtained with the C-5 indicated that significant differences

existed between pressure measurements made in the wind tunnel and flight. Similar

issues had previously arisen during the C-141 program. These issues involved difficulties with scaling effects in wind-tunnel tests. Extensive fundamental research was initiated in the Langley 8-Foot Transonic Pressure Tunnel under the direction of Richard

Whitcomb. The research was initiated to develop an approach of simulating high

Reynolds number flows by using specific placement of artificial boundary-layer trip

strips on the wing upper and lower surfaces of the wind-tunnel model. The test program,

which was conducted by Donald Loving, Arvo Luoma, and James A. Blackwell, Jr., successfully identified a methodology that more properly simulated the appropriate boundary-layer thickness in transonic wind-tunnel tests. This technique was used extensively

in the development of the supercritical airfoil.

Highlights of Research by Langley for the C-130

Lockheed Martin C-130 Hercules 135

Lockheed Martin C-130 Hercules

HIGHLIGHTS OF RESEARCH BY LANGLEY FOR THE C-130

1. Lockheed used aerodynamic computational codes developed by Langley in the configuration development of models of the C-130.

2. Under a Langley contract in the early 1970’s, Lockheed produced an advanced

boron reinforced metal center wing box for the C-130 that was flight tested on three

C-130E aircraft.

3. In the 1980’s, Lockheed tested a composite center wing box for the C-130, which

was not implemented but provided expertise for applications of advanced composites to other Lockheed Martin products, including the F-22.

4. Lockheed, under contract to Langley, developed piloted simulators and interacted

with Langley researchers to develop advanced cockpit liquid crystal flat-panel displays for the C-130J.

SPECIFICATIONS

Manufacturer

Lockheed Martin

Date in service

C-130A . . . . . . . . . . . . .1956

C-130E . . . . . . . . . . . . .1962

C-130J. . . . . . . . . . . . . .1996

Type

Transport

Crew

Three

Engine

Allison T56-A-15 turboprops

USERS

U.S. Air Force (Active, Air 

National Guard, and Reserve), 

U.S. Navy, U.S. Marine Corps, 

U.S. Coast Guard, and over 

65 countries

DIMENSIONS

Wingspan. . . . . . . . . . . 132.6 ft

Length . . . . . . . . . . . . . . 97.8 ft

Height . . . . . . . . . . . . . . 38.4 ft

Wing area. . . . . . . . . 1,745 sq ft

WEIGHT

Empty . . . . . . . . . . . . 75,743 lb

Max takeoff . . . . . . . 175,000 lb

PERFORMANCE

Cruise speed . . . . . . . 360 mph

Range. . . . . . . . . . . . 2,700 n mi
Highlights of Research by Langley for the C-130

136 Lockheed Martin C-130 Hercules

The Lockheed (now Lockheed Martin) C-130 Hercules is arguably the most versatile

military transport aircraft ever built. The aircraft is capable of operating from rough, dirt

strips and is the prime transport for air dropping troops and equipment into hostile areas.

C-130’s fulfill a wide range of operational missions in both peace and war, with specialized versions of the aircraft that perform an enormous number of roles. The C-130J

incorporates state-of-the-art technology to reduce manpower requirements, lower operating and support costs, and provide life cycle cost savings over earlier C-130 models.

Langley’s contributions to the C-130 program include composite structures and materials, noise reduction, cockpit displays, and aerodynamic technologies. Lockheed has

extensively used basic and applied research studies conducted by Langley in the continuous evolution of the C-130. For example, aerodynamic analyses of wing performance,

stall characteristics, and loads have been accomplished with computational methods

developed by Langley. Also, Langley methodology has been used to predict C-130 exterior noise and to reduce interior noise. Lockheed’s participation in the design and development of advanced simulators at Langley and Langley’s research on advanced cockpit

displays led to the adoption of liquid crystal flat-panel displays for the C-130J. The most

interactive Langley and Lockheed studies of the C-130 have occurred in applications of

composite structures and materials. Under Langley sponsored contracts in the 1970’s,

Lockheed fabricated and tested a boron reinforced metal center wing box to improve the

fatigue life by a factor of three and reduce the weight by 300 lb. The modified wing box

was subsequently flight tested on three C-130 aircraft, which are still in routine fleet service. In the 1980’s, a subscale all-composite C-130 center wing box was designed, fabricated, and structurally tested as part of the Langley Advanced Composites Technology

(ACT) Program to validate the potential for increased load levels with reduced weight.

On November 6, 1998, Lockheed Martin arranged for a C-130J to visit Langley for a

special ceremony in honor of NASA’s continuous contributions to the C-130 Hercules.
Langley Contributions to the C-130

Lockheed Martin C-130 Hercules 137

LANGLEY CONTRIBUTIONS TO THE C-130

Composite Structures and 

Materials

Lockheed Martin has had an interest in Langley research on the development of

advanced composite structures for the past 30 years. Working under a long series of

Langley contracts, Lockheed has developed composite flaps, wing trailing edges, and

propellers for the C-130J. As a result of extensive experience from these efforts, Lockheed has also developed composite process improvements for reduced costs.

In 1968, thorough inspections of the Air Force C-130 fleet revealed that almost half of

the 619 aircraft in operational service had fatigue cracks in the center wing section. The

technical community offered numerous recommendations to update and repair this vital

aircraft.

In the 1970’s, Lockheed conducted a five-phase program under a Langley contract to

develop and demonstrate the selective reinforcement of conventional metallic structures

with boron composites. This program, under the direction of Langley researcher

H. Benson Dexter, was designed to demonstrate that advanced filamentary boron composites could improve static strength and fatigue endurance with less weight than would

be possible with metal reinforcement. Contract activities included the development of a

basis for structural design, selection, and verification of materials and processes; manufacturing and tooling development; and fabrication and test of full-scale portions of the

center wing box. The baseline C-130E aluminum center wing box design was modified

by removing aluminum and adding unidirectional boron reinforcing laminates bonded

to the crown of the hat stiffeners in the wing structure. The center wing sections on three

C-130E fleet aircraft with fatigue cracks were replaced with the new stronger aluminum

wing box. This hybrid design improved the fatigue life by a factor of three while reducing the weight by 300 lb over the conventional metallic wing. Flight tests of the modified center wing structure were later conducted on three C-130E fleet aircraft. These

aircraft were entered into routine fleet service in 1974 and are still operational. Unfortunately, the Air Force was not ready to commit to the new technology.

In the 1980’s, Lockheed actively participated in several contracts for the development of

composite wing and fuselage structures that led to the Langley Advanced Composites

Technology (ACT) Program. Working under a Langley contract managed by Randall C.

Davis, Lockheed designed and fabricated a full height, half-chord, all-composite center

wing box for the C-130. This wing box was designed, fabricated, and successfully tested

at the higher load requirements of the special operations aircraft. The resulting wing box

weight was lower than the conventional metal wing box. Funding reductions for the

ACT Program terminated the potential C-130 applications, and the remaining advanced

composite program elements were applied to other aircraft such as the F-22.

Advanced Cockpit Displays Under NASA contract, Lockheed built three individual simulators that are located at

Langley, NASA Ames Research Center, and Lockheed. Interactions with the Langley

staff regarding NASA research on advanced cockpit displays led to the development of

head up display (HUD) technology and liquid crystal flat-panel displays, which provide

integrated instrument information and significantly reduce pilot workload and increase

maneuver precision for the C-130J.

Acoustics As a result of certain mission specific requirements, the external and interior noise characteristics of the C-130 have received considerable attention from Lockheed. The utilization of the aircraft for special missions requires that the exterior noise be minimized.

Likewise, the interior noise for missions that transport combat troops or sensitive instrumentation must be controlled through accurate acoustic analysis. In accomplishing these

tasks, Lockheed used noise prediction and control methods developed by Langley.
Langley Contributions to the C-130

138 Lockheed Martin C-130 Hercules

Aerodynamic Technologies The aerodynamic development of the C-130 by Lockheed included the utilization of

advanced databases of Langley experimental and computational studies. Although no

wind-tunnel tests of the C-130 configuration have been conducted in Langley facilities,

discussions of the interpretation and application of Langley aerodynamic concepts and

data to the C-130 were common during the development of the aircraft. For example,

Lockheed’s interest in providing short takeoff and landing capabilities to the C-130

stimulated discussions on all facets of Langley research on high-lift systems, including

trailing-edge flaps, propeller-induced effects, and powered-lift concepts. Lockheed

remained particularly informed and interested in potential applications of the externally

blown flap (EBF) and the upper-surface blowing (USB) powered-lift concepts conceived and developed at Langley. Numerous discussions with Langley researchers took

place, especially with John P. Campbell and Joseph L. Johnson, Jr. for the EBF concept,

and with Johnson for the USB concept.

Lockheed has applied computational codes developed by Langley to assess and improve

aircraft characteristics, including the stall characteristics of the C-130J. Aerodynamic

loads and several other significant aerodynamic topics have been investigated with the

computational code USM3D, which was developed by Neal T. Frink of Langley.

Another Langley aerodynamic code, FUN2DI, was used by Lockheed to simulate the

effects of leading-edge ice shapes on the C-130J wing and empennage lifting characteristics. In this particular application, the code significantly reduced the number of tests

required to support Federal Aviation Administration (FAA) certification.

Recognition Visit As a gesture of goodwill and recognition of the contributions of all the NASA research

centers (Langley, Ames, Glenn, and Dryden) to the development of the C-130 Hercules,

Lockheed Martin arranged for a visit of a C-130J to the Langley Research Center on

November 6, 1998. The C-130 flew to Langley from the Lockheed Martin facility in

Marietta, Georgia. Langley Director Dr. Jeremiah Creedon welcomed representatives

from Lockheed Martin, Congress, NASA Headquarters, and the Air Force Air Combat

Command, as well as Langley employees in a formal ceremony at the Langley flight

hangar. Mr. James A. (Micky) Blackwell, Jr., President of Lockheed Martin’s Aeronautics Sector, recognized the contributions of NASA employees to the C-130 and the fruitful partnership between NASA and industry that it represented. Mr. Blackwell’s

compliments were especially meaningful to the Langley staff because he began his aerospace career as a NASA employee at Langley in 1962 and worked with Dr. Richard

Whitcomb at the Langley 8-Foot Transonic Pressure Tunnel.

Langley researcher Mary Beth Wusk and her daughter

complete their tour of the C-130J at Langley in 1998.
Highlights of Research by Langley for the C-141

Lockheed Martin C-141 Starlifter 139

Lockheed Martin C-141 Starlifter

HIGHLIGHTS OF RESEARCH BY LANGLEY FOR THE C-141

1. Parametric tests in the Langley 16-Foot Transonic Dynamics Tunnel (TDT) of an

isolated-tail model advanced the understanding of T-tail flutter at transonic conditions.

2. Although the tail design did not flutter in initial TDT tests, the parametric tests identified several issues, including a large area of transonic flow separation at the juncture of the vertical and horizontal tails that promoted early flutter for some

configurations.

3. When an unpredicted elevator-induced flutter problem in flight was exhibited, TDT

tests identified key factors and solutions.

4. The isolated-tail tests permitted flutter clearance for a complete model of the C-141

in subsequent TDT tests.

5. Langley developed a technique to test dynamically scaled models in TDT to assess

an aileron reversal problem.

6. Joint Langley and Air Force runway performance tests with a C-141 aircraft established grooving as an effective solution to hydroplaning accidents.

SPECIFICATIONS

Manufacturer

Lockheed

Date in service

May 1964

Type

Transport

Crew

Six

Engine

Pratt & Whitney TF33-P-7

USERS

U.S. Air Force (Active, Air 

National Guard, and Reserve)

DIMENSIONS

Wingspan. . . . . . . . . . . 160.0 ft

Length . . . . . . . . . . . . . 168.3 ft

Height . . . . . . . . . . . . . . 39.6 ft

Wing area. . . . . . . . . 3,228 sq ft

WEIGHT

Empty . . . . . . . . . . . 140,882 lb

Gross . . . . . . . . . . . . 343,000 lb

PERFORMANCE

Max speed . . . . . Mach number

of 0.83

Range. . . . . . . . . . . . 2,550 n mi
Highlights of Research by Langley for the C-141

140 Lockheed Martin C-141 Starlifter

The Lockheed (now Lockheed Martin) C-141was the first jet aircraft designed to meet

military standards as a troop and cargo carrier. It was also the first military aircraft to be

developed with a requirement for FAA type certification in the contract. The Starlifter is

the workhorse of the Air Mobility Command. It fulfills a vast spectrum of airlift requirements through its ability to airlift combat forces over long distances, place those forces

and their equipment either by conventional landings or airdrops, resupply employed

forces, and extract the sick and wounded from a hostile area. The current C-141B is a

stretched version of the original C-141A with in-flight refueling capability. The C-141B

is about 23 ft longer than the C-141A, with cargo capacity increased by about one-third.

The C-141 force, nearing seven million flying hours, has a proven reliability and longrange capability.

Several critical flutter tests for the C-141 were conducted in the Langley 16-Foot Transonic Dynamics Tunnel (TDT). During these tests, parametric experimental and computational research was conducted on the flutter characteristics of T-tail configurations

with full-span models and unique isolated-tail models of the C-141 configuration. Studies of the aeroelastic mechanisms responsible for inducing flutter led to significant

improvements in the prediction and analysis of T-tail flutter at transonic conditions and

the development of specific modifications to cure flow separation near the intersection

of the vertical- and horizontal-tail surfaces. During early service, the C-141 exhibited

tail flutter that was precipitated by large elevator deflections. This phenomenon was also

replicated and analyzed in the TDT. Langley also conducted research in the TDT to

assess tendencies of the C-141 to exhibit the aeroelastic phenomenon known as highspeed “aileron reversal”.

The C-141 aircraft was a test subject during joint NASA and Air Force runway traction

studies, which demonstrated the effectiveness of a runway grooving concept developed

by Langley. Fifty grooved and ungrooved runway surfaces were tested and grooving

was established as an effective solution to hydroplaning accidents. Subsequently, runways and highways worldwide were grooved for better traction in inclement weather.
Langley Contributions to the C-141

Lockheed Martin C-141 Starlifter 141

LANGLEY CONTRIBUTIONS TO THE C-141

Tail Flutter In the 1950’s, several domestic and foreign high-performance aircraft configurations

were developed that incorporated T-tail empennage configurations. Unfortunately, operational experiences with some of these aircraft indicated that tail flutter could be a critical problem for this configuration at high subsonic speeds. In July 1954, a British

Handley Page Victor bomber experienced severe T-tail flutter and crashed during a lowaltitude, high-speed flight test when the tail began wobbling and then tore off the aircraft, which dove into the ground. Noted aviation periodicals, including Aviation Week,

stated that the accident raised doubts on the high placed T-tail configuration (ref. 6). In

addition, jet-powered T-tail flying boats had been developed for the Navy that also experienced flutter problems.

The staff of the Langley 16-Foot Transonic Dynamics Tunnel (TDT) was cognizant of

the T-tail problem as the C-141 configuration entered the developmental process. The

complex aeroelastic and aerodynamic factors that had allowed tail flutter to occur were

discussed and researched in considerable depth by TDT staff members Frank T. Abbott,

Charles L. Ruhlin, Maynard C. Sandford, and E. Carson Yates, Jr.. The Langley team

and their peers recognized that the flutter mechanisms of T-tails were not well understood, particularly at critical transonic flight conditions where flutter margins were minimal. In addition, they identified certain geometric parameters, such as dihedral and

sweep of the horizontal-tail surfaces, to be particularly critical. Carson Yates conducted

extremely complex analytical calculations that identified the critical parameters and flutter modes for T-tails, and the results of his calculations highlighted the dramatic flutter

challenge for transonic conditions.

A formal request from the Air Force for flutter clearance tests of the C-141 in the

Langley TDT was received. In view of the relatively poor understanding of T-tail flutter,

the Air Force, Lockheed, and Langley team agreed to conduct special tests of a dynamically scaled model of the empennage and rear fuselage in the TDT. These tests

Flutter model of C-141 empennage in the Langley 16-Foot Transonic

Dynamics Tunnel in 1961 with highly streamlined original bullet

fairing at the juncture of the horizontal and vertical tails.
Langley Contributions to the C-141

142 Lockheed Martin C-141 Starlifter

permitted parametric studies and correlation with theory before the full-span model flutter clearance test. Flutter tests of this unique C-141 empennage model began in the TDT

in late 1961. The design configuration did not flutter within the Mach number and

dynamic pressure ranges tested. A matrix of structural parameters and test conditions

was covered to determine the relative sensitivity of flutter to variations in physical features such as the stiffness of the horizontal-tail pitch trim actuator, stiffness of the fin

spar, roll and yaw stiffness of fin-stabilizer joints, rotational stiffness of elevators and

rudder, and stabilizer mass and yaw and roll.

During the isolated-tail tests, the NASA and industry team encountered an unexpected

flow phenomenon on the tail at transonic speeds. The C-141 tail had been designed with

a streamlined bullet-shaped fairing to improve airflow at the juncture of the vertical and

horizontal tails. However, at transonic speeds the bullet shape caused adverse pressure

gradients and shock-induced flow separation over the aft portion of the fin-stabilizer

juncture. Tufts on the vertical tail illustrated the dynamic and massive flow separation

regions as the tail fluttered over relatively large amplitudes. The flow separation acted as

a forcing function to encourage certain flutter modes of the entire tail surface. Yates recommended a redesign of the bullet, including a nonstreamlined shape and a blunt “boat

tail”. Vortex generators on the fin were also evaluated. With the vortex generators and

bullet modifications, results of the test indicated that the vertical-tail flow separation was

entirely eliminated and any tendency for flutter was pushed significantly beyond the

flight envelope.

The results of the isolated-tail model tests significantly increased the understanding of

T-tail flutter prediction, and provided extremely valuable background for the upcoming

flutter clearance test of the complete configuration. When the full-span flutter clearance

C-141 model being prepared for flutter tests in the Transonic Dynamics Tunnel in 1962.
Langley Contributions to the C-141

Lockheed Martin C-141 Starlifter 143

model of the C-141 was tested in the TDT in 1962, no flutter was encountered within the

flight envelope (flutter was pushed beyond 120 percent of design dive speed), and the

value of the isolated-tail model tests was recognized by the participants.

After the C-141 entered service, an unexpected unstable oscillation of the horizontal tail

was experienced during high-altitude flight tests. The flutter was precipitated by a

deflection of about 8 deg of the elevator relative to the stabilizer; no fix was found in

flight tests. Analysis by Lockheed indicated that the flutter speed could be raised significantly by increasing the elevator mass balance, and this approach was used to eliminate

the problem. This elevator-induced flutter mechanism was studied by Maynard

Sandford and Charles Ruhlin with the isolated-tail model in the TDT, where they found

that the flutter was reproduced by the model. The tests also verified the effectiveness of

elevator mass balancing to eliminate tail flutter.

In summary, Langley’s contribution to the C-141 program in the area of flutter generated extensive advances in experimental techniques and analytical methods for fundamental understanding of T-tail flutter characteristics. The highly successful flutter

studies of the C-141 resulted in significant advances in the development of T- tail configurations.

Aileron Reversal Evaluations of the C-141 indicated that for certain flight conditions the aircraft experienced the phenomenon known as aileron reversal. This phenomenon occurs when a

deflection for roll control of the aileron at the wing trailing edge results in aeroelastic

twisting of the wing to the extent that the control effectiveness is nullified or actually

reversed. That is, a pilot’s input to intentionally roll the aircraft results in little or no

response. In some cases, the effects of aileron reversal can actually roll the aircraft in the

direction opposite to that intended by the pilot. Accurate predictions of this phenomenon require precise estimates of the aerodynamic behavior of the wing and aileron system under dynamic conditions and at high speeds. The difficulty of estimating

aerodynamics at transonic conditions made this problem a significant challenge for the

designers of emerging large, flexible transports such as the C-141 and C-5.

C-141 model in Transonic Dynamics Tunnel for aileron reversal tests in 1966.
Langley Contributions to the C-141

144 Lockheed Martin C-141 Starlifter

Langley researcher Irving Abel developed an innovative experimental technique to evaluate aileron reversal tendencies with an aeroelastically scaled C-141 model in the TDT

during 1964 and 1966. Abel used a cable-mount system in the TDT that had been developed by Wilmer H. Reed, Jr. and Frank Abbott to permit more realistic flutter tests by

allowing the structural modes of the models to be simulated in free-flight conditions.

Abel’s results for the C-141 model agreed well with flight results and provided a new

test method to the capabilities of the TDT.

Runway Grooving In the 1950’s, Langley researchers at the Langley Aircraft Landing Dynamics Facility

focused their research on aircraft braking and directional control performance on wet

runway surfaces. This effort was led by Langley researchers Walter Horne and

Thomas J. Yager. The phenomenon of tire hydroplaning was identified as a contributory

factor for unsatisfactory tire traction on wet runways. The associated losses in tire traction in water were defined for a variety of test parameters. A technique that appeared

promising for improved water drainage at the tire and pavement interface was to modify

the pavement surface with slots, or grooves, similar to the grooves in aircraft tire treads.

Basic parametric research on the groove concept was conducted at the Aircraft Landing

Dynamics Facility. The very positive results led to full-scale, instrumented aircraft tests

at the landing research runway at the NASA Wallops Flight Facility in 1968.

In a joint program with the Air Force, Langley evaluated the effects of 50 grooved and

ungrooved runway surfaces on the braking performance of a C-141 aircraft. On the

basis of these test results and other aircraft evaluations, the application of grooving to

runways and the nation’s highways has been accepted as an efficient means for minimizing wet pavement skidding accidents.

Wind Tunnel and Flight 

Correlation

During early flight tests of the C-141, the wing pressures and pitching moments were

found to be considerably different from those predicted in wind-tunnel tests at supercritical Mach numbers. These discrepancies resulted in several national efforts to establish

reasons for the differences, with emphasis on wind-tunnel test procedures. At Langley,

Dr. Richard T. Whitcomb participated in the analysis of the data discrepancy and concluded that wind-tunnel scale effects were the problem. Under the direction of

Whitcomb, Donald L. Loving led a study in 1965 that focused on the impact of

C-141 braking tests in a joint NASA, Air Force,

and FAA program at Wallops Flight Facility.
Langley Contributions to the C-141

Lockheed Martin C-141 Starlifter 145

shock-induced boundary-layer separation. Differences in the relative magnitudes of

shock-induced flow separation resulted in large differences in aerodynamic loads on the

wing. Unfortunately, the phenomenon was difficult to model and extremely complex.

The problem was differences between the relative thickness of boundary layers on models and full-scale aircraft. The importance of artificially locating transition on a model to

produce the same relative boundary-layer thickness at the trailing edge of the wing was

highlighted. However, locating the transition point at the appropriate place on the model

proved to be more an art than a science. The major recommendation from the study was

to conduct wind-tunnel tests for several artificial positions of transition to evaluate the

sensitivity of shock-induced separation to modifications of the boundary-layer conditions. Later, James A. (Micky) Blackwell, Jr. of Langley contributed an approach to

scaling and transition-fixing that was accepted as producing accurate simulations for

wind-tunnel practice.

In a tunnel-to-flight study, Langley awarded a contract to Lockheed in 1970 to conduct

analytical studies on drag estimation for the C-141 and to obtain a set of fully corrected

wind-tunnel data on a 0.0275-scale C-141 model in the Langley 8-Foot Transonic Pressure Tunnel. Lockheed’s experience in the C-5 program with new transition-fixing techniques and model support systems was applied to the C-141 test data to obtain the

accuracy required for the study. Model support interference corrections were evaluated

through a systematic series of tests, and the fully corrected model data were analyzed to

provide details of the model component interference factors. The results of the investigation indicated that the predicted, subcritical minimum profile drag of the complete

C-141 configuration was within 0.7 percent of flight-test data.

C-141 model with dorsal strut and lower strut support in the

8-Foot Transonic Pressure Tunnel for drag correlation studies.

Highlights of Research by Langley for the F-16

Lockheed Martin F-16 Fighting Falcon 147

Lockheed Martin F-16 Fighting 

Falcon

HIGHLIGHTS OF RESEARCH BY LANGLEY FOR THE F-16

1. At the request of industry and Department of Defense, Langley staff participated in

F-16 reviews, from the YF-16 prototype to the current F-16 variants.

2. The F-16 uses Langley wind-tunnel research on leading- and trailing-edge flap technology for transonic maneuver optimization.

3. Langley’s fly-by-wire technology and sidestick controller are incorporated in the

F-16.

4. Lockheed Martin Tactical Aircraft Systems (LMTAS) sought Langley’s guidance

and accepted recommendations for a wing-body strake that provides superior

maneuverability through the aerodynamic phenomenon known as vortex lift.

5. Langley helped solve numerous F-16 developmental challenges including

• Flutter clearance

• Spin recovery

• High-angle-of-attack stability and control

• Recovery from a deep stall

6. Langley provided supersonic wing design methods and developmental tests in a

cooperative program with LMTAS for the F-16XL supersonic cruise prototypes.

SPECIFICATIONS

Manufacturer

Lockheed Martin

Date in service

January 1979

Type

Fighter-attack

Crew

One or Two

Engine

F-16C . . . Pratt & Whitney 

F100-PW-200

. . . General Electric

F110-GE-129

USERS

U.S. Air Force, U.S. Navy, 

Bahrain, Belgium, Denmark, 

Egypt, Greece, Indonesia, Israel, 

South Korea, Netherlands, 

Norway, Pakistan, Portugal, 

Singapore, Taiwan, Thailand, 

Turkey, and Venezuela

DIMENSIONS

Wingspan. . . . . . . . . . . . 31.0 ft

Length . . . . . . . . . . . . . . 49.3 ft

Height . . . . . . . . . . . . . . 16.7 ft

Wing area. . . . . . . . . 300.0 sq ft

WEIGHT

Empty . . . . . . . . . . 18,591.0 lb

Typical combat . . . 23,498.0 lb

PERFORMANCE

Max speed . . . . . . . above Mach

number of 2.0

Radius of action

Air patrol . . . . . . . 866 n mi

Typical strike . . . . 676 n mi
Highlights of Research by Langley for the F-16

148 Lockheed Martin F-16 Fighting Falcon

The conception, development, and deployment of the F-16 by the Lockheed Martin Tactical Aircraft Systems (LMTAS) Division (formerly General Dynamics) included a

close working relationship with Langley Research Center. Throughout the design and

deployment of the F-16, Langley personnel participated in evaluations, wind-tunnel

tests, and special studies—all of which helped to insure superior maneuverability and

performance for this first-line U.S. fighter-attack aircraft. The LMTAS and NASA partnership began with the YF-16 Lightweight Fighter (LWF) Program in 1971. The YF-16

concept of a relatively small, highly maneuverable day fighter ultimately evolved into

the multimission, all-weather F-16, which has been deployed worldwide by numerous

countries. General Dynamics was awarded the Collier Trophy for 1975 in recognition of

accomplishments in the development of the F-16. The F-16, with its primary mission as

a strike aircraft, complements the Air Force F-15 air superiority fighter. The aircraft has

been a workhorse for several nations in recent conflicts including Operation Desert

Storm, Bosnia, and Kosovo.

Designers of the F-16 frequently interacted with the Langley staff and used Langley

facilities during the development cycles for the YF-16 and the F-16. Existing NASA

data and additional cooperative tests were used to optimize aerodynamic performance,

stability and control, and aeroelasticity. Langley facilities used by the LMTAS and

NASA team included the 30- by 60-Foot (Full-Scale) Tunnel, the 20-Foot Vertical

Spin Tunnel, the Unitary Plan Wind Tunnel, the 16-Foot Transonic Dynamics Tunnel,

the 7- by 10-Foot High-Speed Tunnel, and the Differential Maneuvering Simulator.

Langley was involved in research on several variants of the F-16, including the highly

impressive F-16XL, which was a derivative that can cruise efficiently at supersonic

speeds without use of an afterburner. Although not put into production, the F-16XL

demonstrated the validity of Langley design methodologies for supersonic cruise

vehicles.
Langley Contributions to the F-16

Lockheed Martin F-16 Fighting Falcon 149

LANGLEY CONTRIBUTIONS TO THE F-16

Early Assessments In early 1972, the Langley Research Center was requested by the Department of

Defense (DOD) to participate in assessments and tests of competing YF-16 and YF-17

designs for the Air Force Lightweight Fighter (LWF) Program. Langley researchers, as

members of DOD source evaluation teams, assessed technical claims of each of the

competing contractors. The YF-16 configuration underwent extensive wind-tunnel tests

at Langley, especially in the 30- by 60-Foot (Full-Scale) Tunnel, the 20-Foot Vertical

Spin Tunnel, the 7- by 10-Foot High-Speed Tunnel, the 16-Foot Transonic Dynamics

Tunnel, and the Unitary Plan Wind Tunnel. Extensive studies of enhanced control systems for high-angle-of-attack conditions were also conducted in the Langley Differential Maneuvering Simulator (DMS) with pilots from Langley, Lockheed Martin Tactical

Aircraft Systems (LMTAS) Division, and the Air Force. The results of these studies provided information on the capabilities of the YF-16. Following the selection of the YF-16

for production as the F-16 in 1974, the precursor tests served as an excellent knowledge

base for development of the new F-16 fighter.

Transonic Performance The air war experience in Vietnam, where the lack of maneuverability of U.S. fighters at

transonic speeds provided advantages to nimble enemy fighters, was the stimulus for the

YF-16 program. The Air Force and designers of the YF-16 therefore placed great

emphasis on achieving unprecedented transonic maneuver capability with excellent

handling qualities. At that time, Langley researchers under the leadership of Edward C.

Polhamus were conducting in-depth studies in the 7- by 10-Foot High-Speed Tunnel of

approaches to obtain near optimum aerodynamic maneuver performance for wings,

including the use of fixed and variable-camber concepts. Some of the earliest systematic

wind-tunnel tests determined the most effective geometries for leading- and trailingedge wing flaps. In addition, studies were conducted to develop methodologies for the

prediction and minimization of undesirable buffet characteristics. The program was

coordinated with flight tests of actual high-performance fighters at the NASA Dryden

Flight Research Center.

Polhamus and his group (including Edward J. Ray, Linwood W. McKinney, Blair B.

Gloss, and William P. Henderson) provided valuable guidance to the LMTAS design

team. The insight and understanding provided by the broad database from Langley tests

permitted development of the extremely effective leading- and trailing-edge flaps used

by the F-16. The F-16 (and most other high-performance fighters) uses specific schedules of flap deflection with Mach number and angle of attack for superior maneuverability at transonic conditions.

Vortex Lift In the early 1960’s worldwide interest in the phenomenon known as “vortex lift”

increased as a result of aerodynamic studies of highly swept configurations such as the

Concorde supersonic transport. Two events contributed to the initiation of a world-class

Langley vortex-lift research program led by Edward Polhamus.

The first event was a detailed experimental and theoretical study of canard configurations at high subsonic speeds led by researcher Linwood McKinney. McKinney became

interested in the favorable effects of vortex on lift that were demonstrated during development of the Swedish Viggen canard configured aircraft. McKinney’s study indicated
Langley Contributions to the F-16

150 Lockheed Martin F-16 Fighting Falcon

that the favorable effects of the canard trailing vortex on the lifting capability of a closecoupled wing might also be extended to higher angles of attack by the strong leadingedge vortex flow of a slender lifting surface.

The second event that led to the vortex-lift work at Langley was a cooperative Langley

and Northrop study of hybrid wings that centered on the use of relatively large, highly

swept wing extensions at the wing-fuselage intersection to promote strong beneficial

vortex-flow effects.

Stimulated by the promise of this revolutionary aerodynamic concept, Polhamus and his

associates put together a vortex-lift research program that became internationally recognized for its experimental database, analytical procedures, and aircraft applications. In

addition to Polhamus and McKinney, key members of this team included Edward Ray,

William Henderson, John E. Lamar, and James M. Luckring. Their research into the

fundamentals and applications of vortex flows allowed Langley to aid U.S. industry in

the design of highly maneuverable advanced fighters.

The evolution of the YF-16 design at LMTAS included studies of configuration variables such as wing design, maneuvering devices, number and location of engines, control surfaces, number and location of tail surfaces, and structural concepts. As the

configuration options matured, two candidate configurations competed for priority. The

first configuration was a simple wing, body, and empennage design, while the second

design was a twin-tailed, blended-wing body with vertical and horizontal tails on

booms. The LMTAS team selected the best features of both configurations for the final

YF-16 design. After considerations of performance, stability, and control were

addressed, the YF-16 configuration incorporated a rather wide, blended forebody that

produced strong vortices at moderate angles of attack. LMTAS had attempted to weaken

the strength of the vortices by promoting attached flow, but these attempts were not

successful.

A team from LMTAS visited the Polhamus group and requested guidance for control of

the vortical flows emanating from the forebody of the YF-16. In a historically significant meeting, the Langley team suggested that a completely different approach be used

F-16 in a hard turn with wing leading-edge flaps deflected and vortices produced

by the sharp wing-body strakes illustrated by condensation.
Langley Contributions to the F-16

Lockheed Martin F-16 Fighting Falcon 151

to control the vortical flow. Specifically, Langley suggested that the leading edge of the

blended forebody be sharpened to increase (rather than decrease) the strength of the vortices, which could be exploited for additional lift. This modification allowed the forebody vortices to dominate and stabilize the flow field over the aircraft at high angles of

attack, improve longitudinal and directional stability for the single-tail configuration,

and stabilize the flow over the outer wing panels. The LMTAS team accepted the recommendation, and subsequent wind-tunnel tests verified the lift-enhancing effect of the

sharpened wing-body strake. In addition, the sharpened strake significantly reduced buffet intensity at transonic maneuvering conditions. The wing-body strake of the F-16 is

regarded as a key contribution to its success as a maneuvering fighter.

When the YF-16 team analyzed the effects of deflected leading- and trailing-edge flaps

and the sharp-edged wing-body strake on directional stability at high angles of attack,

they found that the stability contributions of a single vertical tail were significantly

enhanced. However, the contributions of twin vertical tails were markedly degraded. As

a result of this analysis, the YF-16 was configured with a single vertical tail. Thus, the

Langley recommendation for a sharpened wing-body strake favorably impacted other

configuration features of the aircraft.

High-Angle-Of-Attack 

Stability and Control

Increased maneuverability for the YF-16 necessitated extended flight at high angles of

attack where aerodynamic deficiencies caused by separated airflow can result in sudden

decreases in stability and controllability. Therefore, special emphasis was placed on

tests in Langley facilities to insure that the YF-16 could provide the pilot with “carefree” maneuverability. Langley facilities used included the Full-Scale Tunnel, the Spin

Tunnel, and the DMS. Helicopter drop-model tests for the YF-16 and the F-16 were not

conducted at Langley because of concurrent resource demands of the B-1 and F-15 programs and the fast pace of the LWF Program.

Researcher William A. Newsom, Jr. with the free-flight model

of the YF-16 used in tests in the Full-Scale Tunnel.
Langley Contributions to the F-16

152 Lockheed Martin F-16 Fighting Falcon

To provide superior handling characteristics at high angles of attack, any undesirable

handling characteristics were pushed out of the operating envelope of the aircraft and

the flight envelope was limited with an advanced fly-by-wire flight control system by

LMTAS. This concept has proven to be highly successful and has been used in all variants of the F-16.

Researchers in the Full-Scale Tunnel conducted exhaustive tests of the YF-16 and the

F-16 configurations at high-angle-of-attack conditions. Data gathered in these studies

identified the aerodynamic contributions of components of the airframe, deficiencies in

stability and control, and potential solutions to these deficiencies. These data also

formed the basis for piloted simulator studies at Langley and LMTAS that helped

LMTAS design the flight control system for critical high-angle-of-attack conditions.

Langley and LMTAS engineers recognized that reliance on the flight control system to

insure satisfactory behavior at high angles of attack required research on the ability of

fly-by-wire control systems to limit certain flight parameters during strenuous air combat maneuvers. The YF-16 and F-16 employ the concept of “relaxed static stability” in

which the aircraft is intentionally designed to be aerodynamically unstable while the

flight control system provides integrated stability by sensing critical flight variables and

making the control inputs required to stabilize the aircraft. Cooperative piloted simulator studies were conducted in the Langley DMS to identify critical control system components, schedules, and feedback gains to stabilize the aircraft and pilot system for the

most demanding maneuvers for high-angle-of-attack conditions. Of particular concern

was the ability of the horizontal tails and longitudinal control system to limit the aircraft’s angle of attack during maneuvers with high roll rates at low airspeeds. Such

maneuvers are critical because rapid rolling maneuvers produce large nose-up trim

changes due to inertial effects, whereas the aerodynamic effectiveness of the horizontal

tails becomes significantly reduced at low airspeeds and high angles of attack.

Under the leadership of Langley researchers Luat T. Nguyen and William P. Gilbert,

extensive studies were conducted in the DMS with pilots from Langley, LMTAS, and

the Air Force. These studies verified the effectiveness of the flight control system and

identified critical maneuvers that would be tested during the flight development program. Gains in the flight control system were modified and incorporated into the aircraft

system. New control elements, such as a yaw rate limiter, a rudder command fade-out,

and a roll rate limiter that maximized the maneuvering envelope with minimal adverse

effects were developed. The DMS was flown by the LMTAS YF-16 and F-16 test pilots

who later flew the prototypes. These pilots cited the accuracy of the preflight predictions

and the valuable training and exposure to potentially hazardous flight-test conditions

provided by the DMS.

Curing Deep Stall Early in Langley research, tests of a YF-16 model in the Full-Scale Tunnel indicated

that if angle of attack was not limited by the flight control system, the aircraft could

pitch up and attain an undesirable trimmed condition at very high angles of attack with

insufficient nose-down aerodynamic control to recover normal flight. The Langley

researchers viewed this “deep” stall as a serious problem that would require significant

research for resolution. The ability of the YF-16 to enter this deep stall was demonstrated in piloted simulation with the Langley DMS and the results were formally

reported to the LMTAS team and the Air Force. Unfortunately, other NASA and industry wind-tunnel tests of YF-16 models contradicted the Full-Scale Tunnel results—indicating that the problem would not exist. The engineering community generally agreed
Langley Contributions to the F-16

Lockheed Martin F-16 Fighting Falcon 153

that the deep stall was not an issue for the F-16. Flight tests of the YF-16 aircraft were

not extensive enough to determine susceptibility to deep-stall phenomenon. However,

the follow-on flight-test program for the F-16 proved that the favorable projections were

wrong and that the deep-stall condition actually existed for the aircraft.

High-angle-of-attack test results obtained on the early production version of the F-16

configuration in the Full-Scale Tunnel showed the same deep-stall trimmed condition

that was noted in the YF-16 results. Again, contradictory wind-tunnel results obtained

elsewhere convinced the engineering community that the aircraft would not exhibit the

problem. However, in subsequent high-angle-of-attack flight evaluations at Edwards Air

Force Base, an F-16 that had been subjected to rapid rolls at diminishing airspeeds in

vertical zoom climbs suddenly entered a stabilized deep-stall condition and the pilot

was unable to recover the aircraft with normal aerodynamic controls. The conditions for

the deep stall agreed very well with predictions based on the earlier test results from the

Langley Full-Scale Tunnel. Fortunately, the test aircraft was equipped with an emergency spin recovery parachute that was deployed to recover the aircraft to normal flight

conditions. This event brought all high-angle-of-attack flight tests of the F-16 to a standstill while a solution to the deep stall could be found.

The excellent correlation of the Langley wind-tunnel data with the events that occurred

in flight and the ongoing evaluation of the F-16 in the DMS at Langley provided the

tools to work the problem. A joint NASA, LMTAS, and Air Force team arrived at

Langley and aggressively sought interim and permanent fixes under Nguyen’s lead.

Working with the evaluation pilots, the team devised a “pitch rocker” technique in

which the pilot pumped the control stick fore and aft thereby setting up an oscillatory

pitching motion that forced the aircraft out of the deep stall and allowed recovery to normal flight. The concept was adopted and validated in the F-16 flight-test evaluation at

Edwards and was incorporated in the flight control system as a pilot selectable emergency mode. A longer term fix was developed in cooperative wind-tunnel tests in the

Full-Scale Tunnel and in LMTAS wind tunnels. The ultimate fix for the problem (which

also improved takeoff performance) was increasing the size of the horizontal tail about

25 percent. This solution has been incorporated in all F-16 production aircraft.

Langley also identified and developed an automatic spin prevention control system concept that could prevent inadvertent spins for the F-16. Nguyen and his group demonstrated the effectiveness of the system with the DMS and analytical studies. The

fundamental elements of the system were further refined by LMTAS and incorporated in

the F-16 fleet.

As a result of Langley supporting analysis and tests, the advanced fly-by-wire flight

control systems of the YF-16 and F-16 were designed with confidence that inadvertent

loss of control incidents that had plagued many earlier fighters would be eliminated.

Spin Recovery The YF-16 and F-16 configurations underwent extensive tests in the Langley Spin Tunnel to determine spin and spin recovery characteristics, especially for the configurations

with external store loadings. In addition, these tests determined the size of emergency

spin recovery parachute that is required for the flight trials. The results of these tests

indicated trends that were fairly typical of high-performance fighters. The models predicted two types of spins—one spin was a relatively well-behaved moderate spin from

which recovery was easily effected, and the second spin was a potentially serious flat

spin at very high angles of attack with poor recovery. The success of the sizing of the

spin recovery parachute was proven in its successful deployment in the unexpected
Langley Contributions to the F-16

154 Lockheed Martin F-16 Fighting Falcon

deep-stall encounter. The parachute can be credited with saving the invaluable test aircraft as well as the pilot. The development and implementation of the production automatic spin prevention system by the Langley and LMTAS team has minimized

operational encounters with spins.

Fly By Wire and Sidestick 

Controller

In 1954, flight tests of the first fly-by-wire aircraft, a modified F9F Panther jet, were initiated at Langley. The primary objective of the tests was to evaluate various automatic

control systems, including those based on rate- and normal-acceleration feedback. However (as is the case in many research investigations), the most valuable result of the

flight test was related to secondary objectives—in this case the introduction and evaluation of fly by wire and a sidestick controller for pilot inputs.

In a serendipitous approach, Langley researchers decided to avoid the relatively large

expense and time required to modify the existing hydraulic flight control system for the

F9F. Instead they chose to implement an auxiliary system based on a fly-by-wire analog

concept and a small (4 in.) sidestick controller mounted at the end of the armrest at the

side of the pilot. The sidestick controller was used as the maneuvering flight controller

throughout the investigation. Rapid and precision maneuvers such as air-to-air tracking,

ground strafing runs, and precision landings were evaluated.

Langley test pilot William L. Alford checks out the side-stick controller in 1954 studies.
Langley Contributions to the F-16

Lockheed Martin F-16 Fighting Falcon 155

The objectives of the flight program were completed with great success, and the information on various types of automatic control feedback was used for numerous aircraft

development programs. However, the very successful use of the rudimentary fly-by-wire

and sidestick controller concepts generated considerable excitement within the research

community, especially those visionaries that anticipated the weight saving advantages

for future aircraft. Additional research was conducted at Langley on these systems,

including the use of a sidestick controller for the Apollo mission. The concept of the flyby-wire control system was later refined and greatly improved in cooperative efforts

between Langley and Dryden that used a modified Vought F-8 Crusader and surplus

Apollo digital computers.

Flutter Clearance Flutter clearance tests of both the YF-16 and F-16 were conducted in the Langley

16-Foot Transonic Dynamics Tunnel (12 tunnel entries for the F-16) under the leadership of Moses G. Farmer, Raymond G. Kvaternik, Jerome T. Foughner, and Frank W.

Cazier. Numerous external store configurations were investigated and several potential

flutter problems were identified and solved. LMTAS requested a large number of flutter

tests to identify critical conditions that would be demonstrated in flight, thereby minimizing very expensive flight-test time. The YF-16 and F-16 did not demonstrate flutter

within their flight envelopes in the tunnel tests, but valuable improvements in flutter

margins were identified. For example, a fuel-usage sequence was established for the

three-bay external tanks that significantly raised the flutter speed. Mass balancing of the

wingtip missile launcher corrected a potential flutter problem with the wingtip missile

and underwing missile combination. Several TDT studies were directed at active flutter

suppression for the F-16 with stores. Beginning in 1979, a joint NASA, General

Dynamics, and U.S. Air Force Wright Aeronautical Laboratories team initiated a series

of tests that continued over an 8-year period. These highly successful studies progressed

through an evaluation of a digital adaptive (no prior knowledge of the aircraft configuration) system. A Langley concept for flutter suppression known as the “decoupler pylon”

was designed and evaluated by Wilmer H. Reed, Jr., Cazier, and Farmer, including flight

tests on an F-16 aircraft; however, the concept was not implemented in the F-16 fleet.

Jerome T. Foughner checks out the F-16 model with external stores

mounted in the 16-Foot Transonic Dynamics Tunnel for flutter tests.
Langley Contributions to the F-16

156 Lockheed Martin F-16 Fighting Falcon

The F-16XL In the mid-1970’s the U.S. Air Force became interested in a fighter aircraft capable of

“supercruise”—the ability to cruise supersonically without an afterburner while retaining respectable maneuver, takeoff, and landing characteristics. The supercruise requirement drove aircraft configurations to highly swept wing platforms. LMTAS appreciated

the fact that the modular construction of the YF-16 allowed for relatively simple

replacement of the outer wing panels and that a supercruiser demonstrator aircraft with

a highly swept wing would undoubtedly attract considerable interest within the Air

Force.

Langley’s staff had developed a research program known as the Supersonic Cruise Integrated Fighter (SCIF) Program under the leadership of Roy V. Harris, Jr. As participants

in previous national and NASA civil supersonic transport programs (SST), the Langley

staff were leaders in the development of databases and design methods for efficient SST

configurations. Several in-house supercruiser fighters were designed and tested across

the speed ranges at Langley. Subsequent to the SCIF program, Langley joined several

industry partners in cooperative, nonproprietary studies of supercruiser configurations.

In 1977 Langley and LMTAS agreed to a cooperative study to design a new crankedarrow wing for the F-16 to permit supersonic cruise capability. Personnel from LMTAS

worked alongside the NASA researchers under the direction of Charles M. Jackson at

Langley during the studies. The project leader for supersonic design was David S.

Miller. The results of the wind-tunnel and analytical studies indicated that a viable wing

could be designed to satisfy the supersonic and transonic requirements. With these

results, LMTAS initiated a company funded development of an F-16 derivative with

supersonic cruise capability. Following the spirit of the previous wing design cooperative venture with NASA, a cooperative agreement was signed for mutual efforts on the

new demonstrator, which was called the Supersonic Cruise and Maneuver Prototype

(SCAMP).

Project engineer Sue B. Grafton with the free-flight model of the F-16XL.
Langley Contributions to the F-16

Lockheed Martin F-16 Fighting Falcon 157

Extensive tests for SCAMP took place in Langley facilities, including the Unitary Plan

Wind Tunnel, the 7- by 10-Foot High-Speed Tunnel, the 16-Foot Transonic Dynamics

Tunnel, the Full-Scale Tunnel, the DMS, the Spin Tunnel, and a helicopter drop model.

During these tests, a team led by researcher Joseph L. Johnson, Jr. identified low-speed

stability and control issues that required modifying the wing apex with a rounded

planform. Research on the SCAMP configuration by Langley researchers identified

numerous advanced concepts for improved performance, including the application of

vortex flaps on the highly swept leading edge for improved low-speed and transonic performance, automatic spin prevention concepts, and optimized wings for supersonic

cruise. The final configuration became known as the F-16XL (later designated the

F-16E), which displayed an excellent combination of reduced supersonic wave drag,

utilization of vortex lift for transonic and low-speed maneuvers, low structural weight,

and good transonic performance. The F-16XL flutter envelope was cleared in the

16-Foot Transonic Dynamics Tunnel by Charles L. Ruhlin without significant problems.

Two (a one-seat and a two-seat) F-16XL demonstrator aircraft were subsequently built

and entered flight tests in mid-1982. In recognition of Langley’s many contributions to

the F-16XL, LMTAS management sent letters of recognition to Langley and senior

NASA management. Marilyn E. Ogburn of Johnson’s group was an invited participant

at flight-test evaluations of the F-16XL at Edwards Air Force Base. The results of flight

tests validated the accuracy of Langley wing design procedures, wind-tunnel predictions, and control system designs based on DMS tests. Unfortunately, the interest in

F-16XL prototype in flight.
Langley Contributions to the F-16

158 Lockheed Martin F-16 Fighting Falcon

supersonic cruise was replaced by an urgency to develop a dual role fighter with ground

strike capability. Although the relatively large wing of the F-16XL carried a significant

amount of weapons, the Air Force ultimately selected the F-15E in 1983 for developmental funding and terminated interest in the F-16XL. 
Highlights of Research by Langley for the F-22

Lockheed Martin F-22 Raptor 159

Lockheed Martin F-22 Raptor

HIGHLIGHTS OF RESEARCH BY LANGLEY FOR THE F-22

1. At the request of industry and the Department of Defense, Langley personnel participated in reviews from the genesis of the Advanced Tactical Fighter (ATF) Program

and the YF-22 Prototype Program to the production F-22.

2. The F-22 utilizes the results of Langley research and development of thrust-vectoring nonaxisymmetric nozzles and afterbody integration for enhanced maneuverability and reduced drag.

3. Langley research of the high-angle-of-attack characteristics of the YF-22 and F-22

proved to be highly accurate and contributed to the outstanding agility and spin

resistance of the configuration.

4. Supersonic drag and performance wind-tunnel measurements by Langley agreed

within 1 percent with flight measurements, which ensured supersonic cruise without

afterburner.

SPECIFICATIONS

Manufacturer

Lockheed Martin

Type

Air superiority fighter

Crew

One

Engine

Pratt & Whitney F119-PW-100

USER

U.S. Air Force

DIMENSIONS

Wingspan. . . . . . . . . . . . 44.5 ft

Length . . . . . . . . . . . . . . 62.1 ft

Height . . . . . . . . . . . . . . 16.4 ft

Wing area. . . . . . . . . . .840 sq ft

WEIGHT

Empty . . . . . . . . . . . . 31,670 lb

Max takeoff . . . . . . . . . 60,00 lb

PERFORMANCE

Max speed . . . . . . . above Mach

number of 1.7
Highlights of Research by Langley for the F-22

160 Lockheed Martin F-22 Raptor

In the late 1980’s, concern arose among military planners about the aging design (first

flight in 1972) of the F-15 and the possible loss of future air superiority of the fighter.

Soviet fighters such as the MiG 29 and Su-27 had demonstrated remarkable maneuverability and performance. In addition, fighter technology had taken enormous strides forward with the introduction of stealth, or low observable, technology. There was also

growing concern over the increased effectiveness of the Soviet air defense system that

posed a highly lethal environment for the F-15. Therefore, the Air Force initiated an

Advanced Tactical Fighter (ATF) Program to develop a replacement for the F-15. The

request for proposals (RFP) was sent to industry in September 1985, and Lockheed and

Northrop were chosen in October 1986 to develop two prototype air vehicles designated

YF-22 and YF-23, respectively. Lockheed teamed with Boeing and General Dynamics,

while Northrop teamed with McDonnell Douglas.

The Air Force asked that Langley provide support for the YF-22 and YF-23 development programs on an as requested, equal basis. Within their program funds and interests, Lockheed requested Langley’s support in two key areas: supersonic cruise

performance and high-angle-of-attack and spin technology. Langley facilities used in

the development of the YF-22 and the F-22 included the Unitary Plan Wind Tunnel, the

30- by 60-Foot (Full-Scale) Tunnel, and the 20-Foot Vertical Spin Tunnel. The ATF Program was initially conducted at the highest levels of classification, and Langley demonstrated once again that it could make significant contributions in a highly controlled

environment.

Langley’s contributions to the development and demonstration of the YF-22 were cited

in a letter of appreciation from the Lockheed Vice President for ATF, James A. (Micky)

Blackwell, Jr. to the Langley Center Director, Richard H. Petersen in March 1991.

Blackwell praised the Langley efforts and support of the YF-22 and cited the accuracies

of Langley wind-tunnel predictions and the dramatic demonstrations of the performance

and agility of the prototype. Follow-on Langley support for the production F-22 was

conducted in these same areas.
Langley Contributions to the F-22

Lockheed Martin F-22 Raptor 161

LANGLEY CONTRIBUTIONS TO THE F-22

The Advanced Tactical Fighter 

(ATF) Program

By the late 1980’s, concern arose among military planners about the aging design (first

flight in 1972) of the F-15 and the possible loss of future air superiority of the fighter.

Soviet fighters such as the MiG 29 and the Su-27 had demonstrated remarkable maneuverability and performance, and were provided to Third World countries. Also, fighter

technology had taken enormous strides with the introduction of stealth, or low observable, technology. There was growing concern over the effectiveness of the Soviet air

defense system, because new surface-to-air missiles posed a highly lethal environment

for the F-15. Therefore, the Air Force initiated an Advanced Tactical Fighter (ATF) Program to develop a replacement for the F-15. Throughout this planning and competitive

period, members of the Langley staff were involved in briefings and discussions with

Department of Defense (DOD), Air Force, and industry teams about technical issues

and concepts to be exploited by the new aircraft. In October 1985, the Air Force issued

the original ATF request for proposals (RFP) to seven competing companies. The next

month, the Air Force revised the RFP to include more stringent low observable requirements. In June 1986, Lockheed, Boeing, and General Dynamics signed a teaming memorandum of agreement, but continued to compete individually for the ATF contract.

Prime contracts were subsequently awarded by the Air Force to Lockheed and Northrop

for the development of flying prototypes. Lockheed’s design was designated the YF-22,

and Northrop’s design was the YF-23.

Value of the Langley Database The YF-22 and F-22 aircraft benefited from basic and applied aeronautics research conducted at Langley over the 20-year period prior to the evolution of the programs. In particular, Langley research in nonaxisymmetric thrust-vectoring nozzles, supersonic

cruise without afterburner, and “carefree” maneuverability with unlimited angle of

attack had produced concepts, data, and assessments of advanced technologies that ultimately provided the YF-22 and F-22 with superior characteristics.

The staff of the Langley 16-Foot Transonic Tunnel had long been recognized as the

world leaders in conceptual research on nonaxisymmetric thrust-vectoring nozzles and

aft-end aerodynamic integration for advanced fighters. Fundamental studies of isolated

nozzle performance and vectoring efficiency were coupled with specific configuration

evaluations during the 1960’s, 1970’s, and 1980’s to the point that risk was considerably

reduced, along with dramatic predictions for improvements in fighter maneuverability,

cruise performance, and takeoff and landing performance.

The contributions of Langley researchers in the prediction and reduction of supersonic

drag were also well recognized, including fundamental theories and design methods to

reduce supersonic wave drag. Langley researchers also participated in in-house and

cooperative studies with industry on supersonic civil and military aircraft. These

researchers, who used the supersonic capabilities of the Langley 4- by 4-Foot Supersonic Pressure Tunnel and the Langley Unitary Plan Wind Tunnel, conducted years of

research that came to fruition in the F-22 Program.

The Langley research program on high-angle-of-attack characteristics of fighter aircraft,

which was initiated in 1969 in response to an alarming number of fighter aircraft accidents due to deficient characteristics, provided proven test techniques, design concepts,

and advanced technology for use by the YF-22 and F-22 design teams. The staffs of the

Langley 30- by 60-Foot (Full-Scale) Tunnel and the Langley 20-Foot Vertical Spin
Langley Contributions to the F-22

162 Lockheed Martin F-22 Raptor

Tunnel worked closely with industry in generic and specific applications of their

technologies.

The YF-22 Program During the ATF competition, the Air Force established that each contracting team could

draw upon NASA’s unique expertise and facilities on an equal basis. The Lockheed

YF-22 team intended to place considerable emphasis on achieving unlimited angle-ofattack capability and supersonic cruise for their design. Lockheed requested tests in the

Langley Unitary Plan Wind Tunnel, Spin Tunnel, and Full-Scale Tunnel in support of

this goal.

In mid-1989, static and dynamic tests of the YF-22 began in the Full-Scale Tunnel under

the direction of Sue B. Grafton to determine stability and control at high angles of

attack. Data was also obtained to develop aircraft control laws. Free-flight tests of a

YF-22 model to determine low-speed longitudinal and lateral-directional response characteristics and departure resistance were also conducted. The Langley Spin Tunnel was

used to determine the spin and recovery characteristics of the YF-22 in 1988 and to validate the geometry of the emergency spin recovery parachute. Tests were also conducted

in the Spin Tunnel to determine rotational aerodynamics during simulated spinning conditions for use in the development of control laws.

The first flight of the YF-22 prototype occurred on September 29, 1990, and the flighttest phase of the competition ended on December 28, 1990.

Free-flight tests of the YF-22 model in the Langley Full-Scale Tunnel in 1990.
Langley Contributions to the F-22

Lockheed Martin F-22 Raptor 163

Letter of Appreciation The success and quality of Langley’s contributions to the YF-22 Program were emphasized in a March 12, 1991, letter from James A. Blackwell (Vice President and General

Manager of the Lockheed ATF Office) to Richard H. Petersen, Director of the Langley

Research Center. In the letter, Blackwell stated

On behalf of the Lockheed YF-22 Team, I would like to express our appreciation of the contribution that the people of NASA Langley made to our successful YF-22 flight test program, and provide some feedback on how well the 

flight test measurements agreed with the predictions from your wind-tunnel 

measurements.

Briefly, the flight test program was an enormous success, and we achieved all 

of our objectives. Between first flight on September 29, 1990, and the last 

flight on December 28, 1990, we flew the two prototypes from 80 knots and 

60 ̊ angle of attack to Mach 2+.

We relied on the NASA Langley Unitary Tunnel to provide the final supersonic 

drag and stability and control data that were used for performance predictions and the flight control law design. We demonstrated supercruise on both 

the GE and P&W-powered prototypes as predicted. The supersonic drag 

determined from flight test agreed within one percent of the predictions that 

were made using the Langley Unitary Tunnel data. The supersonic flying 

qualities were rated excellent; we flew to 15 ̊ angle of attack supersonically; 

and we did 360 ̊ full-stick rolls demonstrating excellent roll rates and roll 

response.

The highlight of the flight test program was the high-angle-of-attack flying 

qualities. We relied on: aerodynamic data obtained in the 30- by 60-Foot FullScale Wind Tunnel to define the low-speed, high-angle-of-attack static and 

dynamic aerodynamic derivatives; rotary derivatives from your Spin Tunnel; 

and free-flight demonstrations in the Full-Scale Wind Tunnel. We expanded 

the flight envelope from 20 ̊ to 60 ̊ angle-of-attack, demonstrating pitch attitude changes and full-stick rolls around the velocity vector in 7 calendar days, 

December 11 to December 17. The reason for this rapid envelope expansion 

was the quality of the aerodynamic data used in the control law design and 

pre-flight simulations.

Without the help of the NASA Langley people and your unique test capabilities, it would have been impossible to complete our YF-22 flight test program 

in the time available. We look forward to working with you and your people 

when we win the Full-Scale Development contract to build the F-22.

The Lockheed, Boeing, and General Dynamics team was announced as the winner of

the ATF competition on April 23, 1991.

The F-22 Program Although not immediately apparent to the uninitiated observer, the external geometry of

the F-22 changed significantly from the YF-22 prototype. Specifically, the wingspan

was increased, the wing leading-edge sweep was decreased, the vertical tails were

reduced in area and moved aft, and the horizontal-tail surfaces were reconfigured. These

changes were considered significant enough to warrant specific tests of the F-22 in the

same unique Langley facilities as the YF-22.

High-angle-of-attack tests of the F-22 were conducted in the Full-Scale Tunnel in 1992,

and spin and rotary-balance tests were conducted in 1993 in the Spin Tunnel. In the

F-22 Program, a free-flight model was not built, and tests in the Full-Scale Tunnel were

limited to conventional static force and dynamic (forced-oscillation) tests.
Langley Contributions to the F-22

164 Lockheed Martin F-22 Raptor

Sue Grafton with the F-22 force test model for the Langley Full-Scale Tunnel.

F-22 model during tests in the Langley Spin Tunnel to determine

the size of emergency parachute required for spin recovery.
Langley Contributions to the F-22

Lockheed Martin F-22 Raptor 165

Performance, stability, and control tests at supersonic speeds were accomplished in the

Langley Unitary Plan Wind Tunnel in 1991.

A contribution from the Langley Spin Tunnel to the F-22 Program involved a relocation

and assessment of the attachment point for the emergency spin recovery parachute.

Evaluations of the original F-22 parachute truss structure and attachment point were

accomplished in 1994; however, the attachment point had to be moved forward a

distance of 3 ft on the full-scale aircraft to clear the exhaust plume of the vectored

engine in afterburner. These tests were urgently requested by the Air Force and

Lockheed to complete the installation on the flight-test aircraft before spring of 1999.

The staff of the Langley Spin Tunnel provided timely and critical contributions, including the fabrication of a new parachute truss for the existing F-22 spin model, conducting

free-spinning tests in the Spin Tunnel, and evaluating a broad range of store loadings

and mass asymmetries.

Vertical-Tail Buffet In collaboration with the F-22 System Program Office and the Air Force Research Lab

at Wright-Patterson Air Force Base, Langley researcher Robert W. Moses conducted tail

buffet tests in the Langley 16-Foot Transonic Dynamics Tunnel. These tests assessed the

vertical-tail buffet environment and explored the potential application of advanced buffet alleviation systems. In these tests, the 13.5-scale model of the F-22 that had been

used for tests in the Full-Scale Tunnel was refurbished with a new starboard flexible

vertical-tail surface that included a rudder driven by a hydraulic actuator. A rigid, portside vertical tail was instrumented with pressure transducers for measurements of

unsteady pressures. 

F-22 model mounted for supersonic test in the Langley Unitary Tunnel.
Langley Contributions to the F-22

166 Lockheed Martin F-22 Raptor

F-22 model with instrumented vertical tails undergoes

buffet tests in the 16-Foot Transonic Dynamics Tunnel.
Highlights of Research by Langley for the P-3

Lockheed P-3 Orion 167

Lockheed P-3 Orion

HIGHLIGHTS OF RESEARCH BY LANGLEY FOR THE P-3

1. Tests in the Langley 16-Foot Transonic Dynamics Tunnel (TDT) identified a catastrophic propeller-whirl flutter that had caused two fatal accidents of the Electra civil

transport on which the P-3 was based.

2. Engine mount modifications suggested by the results of the TDT tests cured the

problem and the Electra (and the derivative P-3) safely completed service without

further flutter issues.

SPECIFICATIONS

Manufacturer

Lockheed

Date in service

July 1962

Type

Antisubmarine warfare

Crew

6 minimum

11 normal

Engine

Allison T56-A-14 turboprop 

USERS

U.S. Navy, New Zealand, 

Australia, Norway, Spain, Iran, 

Japan, Netherlands, and 

Portugal

DIMENSIONS

Wingspan. . . . . . . . . . . . 99.7 ft

Length . . . . . . . . . . . . . 116.8 ft

Height . . . . . . . . . . . . . . 33.8 ft

Wing area. . . . . . . . . 1,300 sq ft

WEIGHT

Empty . . . . . . . . . . . . 67,486 lb

Gross . . . . . . . . . . . . 139,760 lb

PERFORMANCE

Max speed . . . . . . . . . 450 knot

Mission duration . . . . . . . . over

14 hr
Highlights of Research by Langley for the P-3

168 Lockheed P-3 Orion

In late 1958, Lockheed began production of a new four-engine turboprop civil transport

named the Electra. About 170 were subsequently built and supplied mainly to U.S. and

South American airlines. The Navy called for design proposals for a new aircraft to

replace the aging P-2 Neptune for maritime patrol and antisubmarine warfare (ASW) in

August 1957. To save cost and permit service introduction as quickly as possible, the

Navy suggested that a variant of an existing aircraft or one in an advanced design stage

would receive favorable consideration if suitable for the missions. Lockheed proposed a

militarized version of the Electra, and in April 1958, the Navy awarded Lockheed a contract to develop the aircraft. The P-3V Orion entered the inventory in August 1962, and

over 35 years later it remains the Navy’s sole land-based antisubmarine warfare aircraft.

It has gone through one designation change (P-3V to P-3) and three major models:

P-3A, P-3B, and P-3C. The latter model is the only one now in active service. The last

P-3 came off the production line at the Lockheed plant in April 1990.

Langley’s contribution to the P-3 program involved powered-model tests of the predecessor Electra configuration in the Langley 16-Foot Transonic Dynamics Tunnel (TDT).

During 1959 and 1960, two catastrophic Electra accidents occurred with evidence that

the aircraft had experienced violent flutter and the wings had been torn from the aircraft.

Working under great pressure (about 130 Electras were in service at the time), a NASA

and industry team conducted tests in the TDT along with analytical calculations. The

driving mechanism behind the catastrophic structural failure was discovered to be propeller-whirl flutter. The phenomenon of propeller-whirl flutter involves a complex interaction of engine mount stiffness, gyroscopic torques of the engine and propeller

combination, and the natural flutter frequency of the wing structure. The results of the

TDT tests very accurately simulated the Electra scenarios. Based on these results, the

engine mount structure on all Electras was strengthened, and the aircraft (and the derivative P-3) continued in service thereafter with great success and safety.
Langley Contributions to the P-3

Lockheed P-3 Orion 169

LANGLEY CONTRIBUTIONS TO THE P-3

The Lockheed Electra In the fall of 1958, Lockheed began deliveries of a new four-engine turboprop Model

L.188 civil transport to U.S. airlines. The sleek airliner, known as the Electra, set a new

pace for luxury and speed for propeller transports. Over 170 Electras were built by

Lockheed and delivered to U.S. and South American airlines.

In August 1957, the U.S. Navy called for design proposals for a new advanced aircraft

for maritime patrol and antisubmarine warfare (ASW) to replace the aging P-2 Neptune.

The Navy strongly suggested that a variant of an existing aircraft or one in the advanced

design stage be used to save cost and permit rapid introduction into fleet service.

Accordingly, Lockheed proposed a military version of the Electra. In April 1958, the

Navy announced that the Electra derivative had won the competition. Known initially as

the P-3V, the aircraft was redesignated in 1962 as the P-3 Orion. The Orion retained the

wings, tail unit, basic fuselage structure, power plant, and many subsystems of the

Electra, although its fuselage was about 7 ft. shorter than the Electra’s.

Soon after introduction to the civil transport fleet, the Electra suffered two widely publicized fatal accidents with suspicious wreckage that raised concern over the structural

integrity of the aircraft. On September 29, 1959, a Braniff Electra cruising near Buffalo,

Powered model of the Lockheed Electra mounted in the

Langley 16-Foot Transonic Dynamics Tunnel for flutter tests.
Langley Contributions to the P-3

170 Lockheed P-3 Orion

Texas, disintegrated without survivors. Investigation of the dispersal of aircraft wreckage revealed that the left wing had failed and separated from the aircraft in flight. On

March 17, 1960, another Electra crashed in Indiana, with startling similarity to the

Texas accident. Its right wing was found over 11,000 ft from the crash site, which indicated that it had also been torn from the aircraft. Over 130 Electras were operating in the

civil fleet at the time, and authorities immediately reduced the cruise speed of the airliners while the investigation attempted to identify the cause of the fatal crashes.

Langley had recently completed the conversion of the Langley 19-Foot Pressure Tunnel

into the world’s first aeroelastic test tunnel, known as the Langley 16-Foot Transonic

Dynamics Tunnel (TDT). The TDT had just been calibrated, and a 0.125-scale powered

model of the Electra was quickly prepared for flutter tests. Senior researchers I. Edward

Garrick, Philip Donely, Robert W. Boswinkle, and D. William Conner led the planning

for the investigation. Frank T. Abbott and Robert M. Bennett led the experimental work

in the TDT. Wilmer H. Reed, Jr. and Samuel R. Bland led analytical studies to model

and predict the phenomenon.

Lockheed and Langley flutter experts were concerned that the propeller driven Electra

may have exhibited the phenomenon known as propeller-whirl flutter, in which the stiffness of the engine mounts interacts with the gyroscopic torques produced by the engine

and propeller combination. This interaction results in an unstable wobbling motion that

could resonate with natural frequencies of the wing structure and could cause catastrophic flutter of the wing.

The industry and NASA team reduced the stiffness of the outboard engine mounts on

the model and found that the wobbling motion indeed coupled with the natural flutter

frequency of the wings. The fatal resonance could build up and tear the aircraft apart in

30 sec. Based on these results, the engine mounts on all Electra aircraft were strengthened, and the Electra and its derivative P-3 aircraft have since operated safely.
Highlights of Research by Langley for the S-3

Lockheed S-3 Viking 171

Lockheed S-3 Viking

HIGHLIGHTS OF RESEARCH BY LANGLEY FOR THE S-3

1. Flutter clearance was obtained for the S-3 during tests in the Langley 16-Foot Transonic Dynamics Tunnel.

2. Spin and spin recovery characteristics of the S-3 were evaluated and found to be satisfactory during tests in the Langley 20-Foot Vertical Spin Tunnel.

SPECIFICATIONS

Manufacturer

Lockheed

Date in service

February 1974

Type

Antisubmarine warfare, 

antisurface warfare, electronic 

warfare, and antimine warfare

Crew

Four

Engine

General Electric TF34-GE-400

USER

U.S. Navy

DIMENSIONS

Wingspan. . . . . . . . . . . . 68.7 ft

Length . . . . . . . . . . . . . . 53.3 ft

Height . . . . . . . . . . . . . . 22.8 ft

Wing area. . . . . . . . . . .598 sq ft

WEIGHT

Empty . . . . . . . . . . . . 26,864 lb

Max takeoff . . . . . . . . 52,539 lb

PERFORMANCE

Max speed . . . . . . . . .450 knots

Range. . . . . . . . . . . . 2,300 n mi
Highlights of Research by Langley for the S-3

172 Lockheed S-3 Viking

Lockheed (now Lockheed Martin) S-3 Viking aircraft are tasked by carrier battle group

commanders to provide antisubmarine warfare (ASW), antisurface warfare (ASUW),

surface surveillance and intelligence collection, electronic warfare, mine warfare, coordinated search and rescue, and fleet support missions such as airborne refueling. The

S-3B aircraft carries surface and subsurface search equipment with integrated target

acquisition and sensor coordinating systems that can collect, process, interpret, and

store ASW and ASUW sensor data. It has a direct attack capability with a variety of

armament, including the Harpoon missile.

During operation Desert Storm, the versatility of the S-3 enabled it to serve a variety of

roles. It flew hundreds of sea surveillance missions to enforce the economic blockade of

Iraq and secure the seas surrounding the battle groups. Mine detection was an especially

critical mission in the Persian Gulf, and the S-3 also served as the primary logistic transport for carriers. The S-3 had a direct combat role in which it electronically monitored

active missile sites prior to air strikes. It also participated in the hunt for Scud missiles.

Perhaps the most important contribution of the S-3 during the conflict was its airborne

tanking capability. In this role, it employed a hose-and-drogue refueling system that

resulted in more efficient refueling operations and more U.S. aircraft getting to their targets. In recognition of its broad applications, the designation of the S-3 Viking squadrons has been changed from Air Antisubmarine Squadron to Sea Control Squadron.

At the request of the Navy, Langley conducted wind-tunnel tests to provide flutter clearance and spin recovery evaluations for the S-3 prior to flight tests. The phenomenon of

aileron “buzz” was encountered in the flutter test and eliminated, and flutter clearance

was successful. Results of the spin tests indicated satisfactory characteristics, and no

major modifications were made to the aircraft. Based on the data from the Langley tests,

Lockheed and the Navy were able to proceed into flight-test development of the S-3

with increased confidence.

Langley facilities used in support of the development of the S-3 were the Langley

16-Foot Transonic Dynamics Tunnel and the Langley 20-Foot Vertical Spin Tunnel.
Langley Contributions to the S-3

Lockheed S-3 Viking 173

LANGLEY CONTRIBUTIONS TO THE S-3

Background In 1964, the Navy announced a requirement for a new carrier-based antisubmarine warfare aircraft (designated VSX) to replace the aging Grumman S-2 Tracker. The new aircraft was to have twice the speed, range, and altitude capability of the S-2. Development

of the S-3 Viking began in 1969 when Lockheed was awarded the VSX contract.

Remarkably, only five years elapsed from the time of contract award until the first aircraft was delivered to a fleet squadron in 1974.

With the decline of the Soviet Union, and a subsequent reduction in the submarine

threat to the U.S. fleet, the S-3 took on many new missions, including antisurface warfare, electronic surveillance, and airborne refueling.

Spin Tunnel Tests In 1972, spin and spin recovery evaluations of the S-3 configuration were conducted in

the Langley 20-Foot Vertical Spin Tunnel by Henry A. Lee and W. Louis White. Results

of the tests indicated satisfactory characteristics would be expected of the S-3, and no

modifications to the basic design were recommended. Although numerous stalling tests

of the S-3 were conducted during the full-scale flight-test development program, intentional spins were not deemed necessary and were not attempted.

Operationally, the S-3 has not experienced stall-departure or spin problems.

S-3 model launched into the vertically rising airstream in the Langley Spin Tunnel.
Langley Contributions to the S-3

174 Lockheed S-3 Viking

Flutter Tests Langley researchers Jean Gilman, Moses G. Farmer, and Charles L. Ruhlin conducted

flutter tests of the S-3 in the Langley 16-Foot Transonic Dynamics Tunnel in late 1970

and early 1971. During the tests, the condition known as aileron “buzz” was encountered in which the S-3 ailerons exhibited very high frequency undamped oscillations.

The problem was solved with a design modification to balance the ailerons, and flutter

clearance for the complete configuration was demonstrated in mid-1971.

S-3 flutter model in the Langley 16-Foot Transonic Dynamics Tunnel.
Highlights of Research by Langley for the F-4

McDonnell Douglas F-4 Phantom II 175

McDonnell Douglas F-4 Phantom II

HIGHLIGHTS OF RESEARCH BY LANGLEY FOR THE F-4

1. Studies in the Langley Unitary Plan Wind Tunnel revealed that the configuration

exhibited lateral-directional stability problems at supersonic speeds, which resulted

in McDonnell redesigning the wing and vertical tail.

2. Langley conducted studies of the stall departure and flat spin and identified causes of

the poor stall-spin behavior of the F-4.

3. Langley, McDonnell Douglas, the Air Force, and the Navy investigated wing modifications to improve the maneuverability and handling characteristics, which resulted

in incorporation of leading-edge slats on later versions of the aircraft.

4. Langley provided a solution to a severe nose buffet problem for the reconnaissance

version.

5. Langley and Air Force braking performance tests conducted with an F-4 aircraft

established runway grooving as an effective solution to hydroplaning accidents.

SPECIFICATIONS

Manufacturer

McDonnell Douglas

Date in service

December 29, 1960

Type

Fighter

Crew

Two

Engine

General Electric J79-GE-17

USERS

U.S. Navy, U.S. Marine Corps, 

U.S. Air Force, Egypt, Israel, 

Iran, Greece, Spain, Turkey, 

South Korea, West Germany, 

Australia, Japan, and Great 

Britain

DIMENSIONS

Wingspan. . . . . . . . . . . . 38.4 ft

Length . . . . . . . . . . . . . . 63.0 ft

Height . . . . . . . . . . . . . . 16.6 ft

Wing area. . . . . . . . . . .530 sq ft

WEIGHT

Empty . . . . . . . . . . . . 31,360 lb

Gross . . . . . . . . . . . . . 58,000 lb

PERFORMANCE

Max speed . . . . . Mach number

of 2.0
Highlights of Research by Langley for the F-4

176 McDonnell Douglas F-4 Phantom II

The McDonnell Douglas (now Boeing) F-4 was an exceptional fighter aircraft, which

was used for air superiority, interdiction, and close air support. Originally developed by

the Navy as a supersonic fleet defense fighter, the F-4 was also put into service by the

Air Force and served a variety of roles in the Vietnam conflict. The final application of

the F-4 by the U.S. was in the “Wild Weasel” role for suppressing enemy air defense

systems. F-4 production ended in 1979 after over 5,000 had been built—more than

2,600 for the U.S. Air Force, about 1,200 for the U.S. Navy and U.S. Marine Corps, and

the rest for friendly foreign nations. Later versions of the aircraft were in the U.S. Air

Force inventory until December 1995. They are still flown by other nations.

NASA Langley Research Center contributions to the F-4 program began during the

design stages when supersonic wind-tunnel tests at Langley identified stability issues

that required redesign of the airframe, including adding dihedral (angle between horizon

and wing panels from frontal perspective) to the outer wing panels and increasing the

size of the vertical fin. Another contribution from Langley resulted in the development

and incorporation of wing leading-edge slats for enhanced maneuverability and

increased safety for high-angle-of-attack conditions.

Langley facilities used in the development and support of the F-4 program included the

Langley Unitary Plan Wind Tunnel, the 30- by 60-Foot (Full-Scale) Tunnel, the 20-Foot

Vertical Spin Tunnel, the 16-Foot Transonic Dynamics Tunnel, the 7- by 10-Foot HighSpeed Tunnel, piloted simulators, and radio-controlled drop models.
Langley Contributions to the F-4

McDonnell Douglas F-4 Phantom II 177

LANGLEY CONTRIBUTIONS TO THE F-4

Early Configuration 

Development

In 1954, the Navy selected McDonnell Aircraft to design and develop an all-weather

supersonic fighter. The fighter, designated the F4H, was to be a fleet defense fighter that

could take off from an aircraft carrier, have a cruise distance of 250 mi, intercept intruders, and then return to the carrier 3 hr after takeoff. The aircraft was to be armed with

missiles and would not carry guns. It would operate as a high-speed (Mach number of

2), standoff missile launcher that would not engage in close-in combat.

In mid-1955 the full-scale engineering mock-up of the twin-engine aircraft featured a

swept wing with no dihedral, and the horizontal tails drooped down at an angle of

15 deg. At the request of the Navy, tests began in the Langley Unitary Plan Wind Tunnel

under the direction of Melvin M. Carmel to determine the supersonic performance and

stability and control characteristics of the original configuration. Three separate entries

in the Unitary Tunnel were made to evaluate the early F4H design.

Results of the first phase of tunnel tests indicated that the F4H exhibited serious deficiencies in lateral-directional stability characteristics at supersonic speeds, including

unstable dihedral effect and marginal directional stability. To cure these problems,

McDonnell introduced 12 deg of geometric dihedral into the outer wing panels (which

were foldable for carrier operations) and increased the size of the vertical tail. Analysis

had indicated that only 3 deg of geometric dihedral across the entire wing would solve

the problem, but the same effect was achieved with less redesign and developmental

effort by changing the outboard panels. Additional tests in other wind tunnels had indicated an undesirable pitch-up characteristic at transonic and low speeds, which was

solved by adding chord to the outer wing panels (producing a leading-edge snag or “dog

tooth”) and by increasing the droop of the horizontal tail to 23 deg. The final phases of

the F4H study in the Unitary Tunnel were directed to the integration of external stores at

supersonic speeds.

Engineering mock-up of the original F4H Phantom without

dihedral in outer wings and 15-deg droop of the horizontal tail.
Langley Contributions to the F-4

178 McDonnell Douglas F-4 Phantom II

After the development process, the F4H was placed into operations with the U.S. Navy

and Marines under the new designation F-4 and set several speed and altitude records.

The Air Force began to acquire F-4’s in 1962, and this famous fighter became a mainstay in the air forces of friendly nations, with several variants produced by the

McDonnell Douglas Corporation.

Maneuverability During the first few years of the Vietnam conflict, the U.S. found itself engaging enemy

aircraft such as the MiG-17 and MiG-19 that were relatively agile and could easily outmaneuver the heavier U.S. aircraft (F-4 and F-105) that had been designed without

requirements for close dogfighting or close weapons such as a gun. Initial tactics used

by U.S. pilots to try and turn with enemy aircraft had been relatively unsuccessful, and it

had become apparent that missiles in use at that time were relatively unreliable at long

ranges. Pilot training and revised tactics were ultimately employed to blunt the threat

and use U.S. aircraft to an advantage, but the lack of maneuverability and a gun for

close-in combat became issues for the Air Force. A new Air Force version known as the

F-4E was equipped with a nose mounted M61 cannon, and additional deliveries to the

Air Force began in October 1967.

McDonnell Douglas became interested in wing modifications for the F-4 that would

improve buffet onset and increase lift and turning performance, while retaining satisfactory characteristics for approach and landing. Langley researcher Edward J. Ray led a

cooperative Langley, McDonnell Douglas, and Air Force study of F-4 maneuver and

buffet characteristics in the Langley 7- by 10-Foot High-Speed Tunnel in 1969. Candidate configurations included the use of wing leading-edge flaps, leading-edge camber,

trailing-edge flaps, and other devices; however, the most effective modification was a

two-position leading-edge slat. Two slats were mounted on the leading edge of each

wing panel in place of the earlier leading-edge flap. The inner slat was fully retractable

at high speeds, but the outer slat remained deployed in both the cruise and high-lift configurations. With the slats deployed, the F-4 could make tighter turns, and approach

speeds were also reduced by a significant amount. Another benefit of this modification

was a dramatic improvement in the lateral-directional handling characteristics and spin

resistance at high angles of attack.

F4H model after modifications with dihedral

in outer wings and increased vertical tail.
Langley Contributions to the F-4

McDonnell Douglas F-4 Phantom II 179

The slat configuration was evaluated during flight tests (known as Project Agile Eagle)

of a modified F-4 test aircraft with extremely impressive results. The wing leading-edge

slats were incorporated on all F-4E aircraft built during and after 1972. Later, the Navy

received a slat equipped version of the aircraft known as the F-4S.

The F-4G Advanced Wild Weasel, which inherited most of the features of the F-4E

including the wing slats, was one of the last versions of the F-4. Working in “hunterkiller” teams of two aircraft, such as F-4G and F-16C, the F-4G hunter could detect,

identify, and locate enemy radar then direct weapons to ensure destruction or suppression of the radar. The technique was effectively used during Operation Desert Storm

against enemy surface-to-air missile batteries.

High-Angle-of-Attack Stability Military strategists had procured the F-4 design as a standoff missile launcher with no

requirement for strenuous maneuvering at high angles of attack. At that time, the need

for close-in air combat maneuvering was thought to be obsolete, due to the advent of

air-to-air missiles. Operations prior to Vietnam had stressed the supersonic mission for

the F-4, and the initial safety record for the aircraft was extremely good.

The return of close-in air-to-air combat during Vietnam unfortunately exposed a deficiency in the flying characteristics of the F-4. During hard turns to engage or escape

enemy aircraft, pilots began to fly the F-4 at high angles of attack where they experienced a marked deterioration in lateral-directional stability and control characteristics.

F-4E model in the Langley 7- by 10-Foot High-Speed Tunnel for evaluation

of wing leading-edge modifications for enhanced maneuverability.
Langley Contributions to the F-4

180 McDonnell Douglas F-4 Phantom II

Inadvertent loss of lateral-directional control and spin entries occurred, with an alarming number of accidents and losses of crew and aircraft during training and combat. The

Navy, Marine Corps, and Air Force suffered over 100 high-angle-of-attack and stallspin accidents over the lifetime of the F-4 aircraft.

In 1967, representatives from the Air Force Aeronautical Systems Division met with

Langley researchers Edward C. Polhamus and Joseph R. Chambers to discuss the growing concern over the high-angle-of-attack and stall-spin accidents (at that time, about

10 aircraft had been lost). Analysis of the problem by the Air Force was particularly difficult because the limited interest in high-angle-of-attack maneuvers had resulted in no

wind-tunnel tests (other than spin tunnel tests) of the F-4 configuration for such conditions. Langley agreed to conduct diagnostic high-angle-of-attack wind-tunnel tests of

the F-4. Tests in the Langley 12-Foot Low-Speed Tunnel and the Langley 30- by

60-Foot (Full-Scale) Tunnel thoroughly documented the aerodynamic factors that produced the loss of lateral-directional stability at high angles of attack.

Chambers and Sue B. Grafton conducted two free-flight model investigations of the F-4

for high-angle-of-attack conditions in the Full-Scale Tunnel. In the first study, flight

tests of a model of the Air Force F-4C demonstrated an abrupt loss of directional stability (nose slice) near wing stall, and most of the flights ended with the model going out of

control. Analysis of wind-tunnel data indicated that massive flow separation on the

swept wing caused adverse flow fields at the tail, thereby degrading the stabilizing influence of the vertical fin at high angles of attack. No simple fixes could be found for the

problem, short of a redesign of the wing.

When interest in wing leading-edge modifications for enhanced maneuverability

became known, Langley conducted free-flight tests of a model of the later F-4E configuration. The test program, which was conducted by Edward Ray in the 7- by 10-Foot

High-Speed Tunnel, was closely monitored. The results obtained from the Full-Scale

Tunnel by Chambers and Grafton for high-angle-of-attack characteristics were fed back

Researcher Sue Grafton with the slatted F-4E model used for

free-flight tests in the Langley Full-Scale Tunnel.
Langley Contributions to the F-4

McDonnell Douglas F-4 Phantom II 181

to Ray and others interested in maneuver performance. The results of the free-flight

model test indicated that the incorporation of wing leading-edge slats markedly

improved the high-angle-of-attack behavior of the F-4 by eliminating the severe nose

slice tendency of the basic configuration.

Langley also conducted studies on the high-angle-of-attack characteristics of the F-4

with a radio-controlled model and a piloted simulator. The radio-controlled model was

used by Charles E. Libbey to determine aircraft motions after loss of control at high

angles of attack and to demonstrate the beneficial effects of the leading-edge slat modification. The simulator study of the F-4 by Frederick L. Moore was one of the first

attempts to develop a simulator to study high-angle-of-attack behavior. The application

of piloted simulators to this area is now a routine development tool.

The Flat Spin Tests of an F-4 model by James S. Bowman, Jr. in the Langley 20-Foot Vertical Spin

Tunnel in the early 1960’s indicated that the F-4 configuration would exhibit several

types of spins. In addition, the recovery characteristics from these various types of spins

differed greatly. For example, one spin involved a relatively steep nose-down fuselage

attitude with large oscillations in roll during the spin motion. Recovery from this spin

was relatively easy with normal pilot control inputs. In contrast to this spin recovery, the

F-4 also exhibited a relatively fast, flat spin in which the aircraft descended vertically in

a rapid spin motion with an almost horizontal (flat) fuselage attitude. Recovery from the

flat spin with normal aircraft controls was found to be impossible. During these spin

tests, Langley determined that a 30-ft diameter emergency spin recovery parachute

would be required for the test aircraft.

F-4 drop model mounted on the Langley helicopter drop rig for a spin entry test.
Langley Contributions to the F-4

182 McDonnell Douglas F-4 Phantom II

Spin tunnel tests are conducted by hand launching a model into a vertically rising airstream with an artificial spinning motion. The question remains as to whether the aircraft could enter such spinning conditions from conventional flight. Langley, therefore,

conducts outdoor radio-controlled drop-model tests to evaluate this tendency. Drop tests

were considered mandatory to confirm the potential for flat spins for the F-4. Fortunately, the results of the radio-controlled F-4 drop-model tests by Libbey indicated that

the aircraft would have a dominant tendency to enter a steeper, recoverable spin rather

than the flat, unrecoverable spin. In fact, the flat spin was only obtained once in over

20 aggressive attempts to spin the drop model.

The Navy and Air Force both conducted full-scale aircraft spin tests of the F-4, with

aggressive control inputs to seek out the various spin modes. The Navy had expressed

doubts over the existence of the flat spin at the beginning of their F-4 spin program. The

agreement of the precursor Langley Spin Tunnel tests with the flight tests was remarkable. The steep, oscillatory spin mode was normally encountered and recovery was satisfactory as predicted by the Spin Tunnel tests. Unfortunately, the fast, flat

unrecoverable spin was encountered in both test programs. The respective test aircraft

were lost in crashes at Patuxent River Naval Air Station, Maryland, and Edwards Air

Force Base, California, when the emergency spin parachute systems failed to operate

properly. In the case of the Navy tests, the parachute failed to inflate properly, while in

the Air Force tests, the mechanical system malfunctioned and released the parachute

prematurely.

Although accident statistics for the F-4 indicated that the accidents involved about an

equal number of approach-to-landing and up-and-away maneuvers, the Air Force and

Navy expressed great interest in determining what features or factors of the F-4 were

responsible for the unrecoverable flat spin mode. A request was made to Langley for

assistance in determining these factors, and a contract was given to McDonnell Douglas

to analytically study the flat spin.

During tests of the F-4 in the Full-Scale Tunnel, Chambers noted that a prospin yawing

moment existed for the configuration at the attitudes associated with the fast, flat spin.

Results from these tests also indicated that the prospin tendencies were produced by the

aft end of the aircraft. An innovative, inexpensive test was used by Langley to identify

the responsible aircraft components and the primary mechanism of the flat spin.

Chambers mounted a commercially available 1/48-scale plastic hobby model of the F-4

on a spindle assembly with a shaft through the top of the fuselage. The model was free

to rotate as it would in a flat spin. When the hobby model was tested in the wind tunnel

in a simulated flat spin attitude, researchers found that it would immediately spin up to

the angular rates exhibited by the spin tunnel model and that the hobby model would do

this to the right or left when released from a nonrotating condition. The researchers

found that the driving mechanism for the flat spin tendency was adverse aerodynamic

interactions between the drooped horizontal tail and the vertical fin. When the drooped

tails were inverted (that is, the tails had 23 deg of positive geometric dihedral) the model

would no longer accelerate into the spin condition and would stabilize without rotating.

The results of the hobby model tests were checked out in the Langley Spin Tunnel with

the dynamically scaled F-4 model previously used for spin tests. The initial tests were

conducted with the baseline F-4 configuration, and as expected, the model exhibited the

fast flat spin. However, when the horizontal tails were inverted, the model would no

longer spin flat, even though it was hand launched with conditions associated with the

fast flat spin. Instead, the model would nose down into the steeper, recoverable spin. It
Langley Contributions to the F-4

McDonnell Douglas F-4 Phantom II 183

was also found that increasing the deflection angle of the horizontal tail to 55 deg or

greater eliminated the prospin aerodynamic interference effect for the basic configuration, which would no longer spin flat.

The results of these tests to identify the cause of the flat spin and other concepts identified by Langley (including an automatic spin prevention control system) were evaluated

by the military. The recommended modifications to the F-4 fleet were considered too

drastic at that time in the operational life of the aircraft, but the important adverse effect

of the tail interference phenomenon was noted for subsequent aircraft development

programs.

In the mid-1980’s, the Navy approached Langley with reports that Marine pilots were

recovering from flat spins by lowering the landing gear. The Navy requested spin tunnel

tests and funded an F-4S model to determine the effects of operating the landing gear

during the flat spin. Spin tunnel tests by Bowman showed that lowering the gear actually

increased the spin rate in the flat spin! Based on these tests, the Navy did not incorporate

lowering the gear as a spin recovery technique in the pilot handbook. Perhaps the most

significant result from this test was that it alerted researchers to the potential adverse

effects of components such as landing gear, gear doors, and weapons bay doors on spin

recovery. The effects of such components had not been routinely tested in decades. This

experience later proved very valuable during other programs.

The contributions and participation of Langley in the F-4 high-angle-of-attack and stallspin efforts are also noteworthy because they formed the impetus within Langley to

form a cohesive suite of test techniques designed to extract the maximum amount of

information in this difficult and complex area. Following the F-4 program, Langley

greatly increased commitments to this area and embarked on a research program with

industry and DOD that has benefited the development of high-performance U.S. aircraft

to this day.

Nose Vibrations In late November 1965, the staff of the Langley 16-Foot Transonic Dynamics Tunnel

(TDT) was urgently requested to assist the Air Force with a buffet problem that was

experienced by the RF-4 reconnaissance version of the aircraft during combat operations in Vietnam. When pilots attempted to perform high-speed pre- and post-strike photographic reconnaissance missions, they found that the nose mounted cameras in the

RF-4 were being literally shaken to pieces, seriously degrading the clarity of the photographic information and ruining the mechanical operations and operational lifetime of

the cameras. Langley researchers Robert V. Doggett and Perry Hanson conducted windtunnel tests of the front fuselage of an RF-4 model in the TDT in early 1966 to measure

fluctuating pressures in the area near the camera lens and housing. The results of the

study indicated that aerodynamic flow separation on the lower forebody over the camera

installation produced large vibratory loads that were the source of the problem. Doggett

and Hanson, working with McDonnell Douglas and the Air Force, developed a modified

camera ramp angle and revised camera enclosure fairing that eliminated the problem

and was incorporated on later models of the RF-4. The fairing, which rounded the flat

lower surface of the baseline nose, also resulted in increased internal nose volume and

allowed larger cameras to be utilized.
Langley Contributions to the F-4

184 McDonnell Douglas F-4 Phantom II

Runway Grooving In the 1950’s, Langley researchers at the Aircraft Landing Dynamics Facility focused

their research on aircraft braking and directional control performance on wet runway

surfaces. This research, led by Langley researchers Walter Horne and Thomas J. Yager,

included ground handling tests of an F-4 test aircraft. Comparative tests of the effects of

runway grooving on braking and handling characteristics provided clear demonstrations

of the effectiveness of the grooving concept.

The RF-4 reconnaissance version of the F-4 with camera

fairing under the forward nose section.

Simplified model of RF-4 nose tested in the Langley 16-Foot Transonic Dynamics Tunnel.
Highlights of Research by Langley for the F-15

McDonnell Douglas F-15 Eagle 185

McDonnell Douglas F-15 Eagle

HIGHLIGHTS OF RESEARCH BY LANGLEY FOR THE F-15

1. At the request of the Department of Defense, Langley responded to a request for proposals with candidate fighter configurations of which one, known as LFAX-8,

strongly influenced the winning design by McDonnell Douglas.

2. Langley conducted over 6,000 wind-tunnel test hours to collect data for the competitive source selection team and participated in the evaluation process.

3. Langley conducted studies to improve the subsonic cruise efficiency with emphasis

on propulsion integration, which resulted in a substantial improvement in performance by the removal of ventral fins and modification of the vertical tails.

4. Langley conducted studies of high-angle-of-attack and spin characteristics to

develop and demonstrate a high level of spin resistance.

5. Tests in the Langley 16-Foot Transonic Dynamics Tunnel identified potential flutter

of the horizontal tails, which resulted in modifications of the tail geometry and subsequent flutter clearance.

6. Langley provided technology, expertise, and facility support for upgrades to the F-15

fleet on a continual basis including development of the F-15E and the F-15 short

takeoff and landing and maneuver technology demonstrator (STOL/MTD).

SPECIFICATIONS

Manufacturer

McDonnell Douglas

Date in service

November 1974

Type

Air superiority, dual role

Crew

One or two

Engine

F-15C . . . Pratt & Whitney

F100-PW-220

USERS

U.S. Air Force, Israel, Saudi 

Arabia, and Japan

DIMENSIONS

Wingspan. . . . . . . . . . . . 42.8 ft

Length . . . . . . . . . . . . . . 63.8 ft

Height . . . . . . . . . . . . . . 18.5 ft

Wing area. . . . . . . . . . .608 sq ft

WEIGHT

Empty . . . . . . . . . . . . 40,000 lb

Typical combat . . . . . 68,000 lb

PERFORMANCE

Max speed . . . . . . . above Mach

number of 2.0

Unrefueled. . . . . . . . 3,450 n mi

range
Highlights of Research by Langley for the F-15

186 McDonnell Douglas F-15 Eagle

One of the most illustrative examples of the benefit of NASA aeronautical research for

military aircraft is the impact of NASA studies on the F-15 air superiority fighter. NASA

studies ranged from conceptual configuration studies that employed aggressive technologies to developmental studies of aerodynamic performance, high-angle-of-attack and

spin characteristics, flutter, and advanced derivative aircraft. Langley facilities used in

the F-15 studies included the Langley 30- by 60-Foot (Full-Scale) Tunnel, the Langley

20-Foot Vertical Spin Tunnel, the Langley 4- by 4-Foot Supersonic Pressure Tunnel, the

Langley Unitary Plan Wind Tunnel, the Langley 16-Foot Transonic Tunnel, the Langley

16-Foot Transonic Dynamics Tunnel, and the Langley 7- by 10-Foot High-Speed

Tunnel.

In 1968, the Department of Defense (DOD) asked NASA to respond to the F-15 request

for proposals (RFP) in a manner similar to the contractors to define the possible impact

of advanced technology on the industry proposals. Under Langley’s leadership, a NASA

team of about 70 professionals colocated at Langley designed a series of advanced fighters that would meet the F-15 mission requirements. One of these configurations,

LFAX-8, was of great interest to the McDonnell Douglas proposal team, which adopted

many of the configuration features in the winning F-15 design.

Langley also participated in the source selection process by conducting over 6,000 test

hours in eight wind tunnels to define the characteristics of competing F-15 designs and

serving on the source selection evaluation board. During the development of the F-15,

Langley provided continuing advice to the Air Force and provided a member to the F-15

Program Office. Langley’s contributions to the F-15 in the areas of aerodynamics, propulsion integration, stability and control, aeroelasticity and flutter, and flight controls

have helped the nation maintain superiority in advanced fighter aircraft.
Langley Contributions to the F-15

McDonnell Douglas F-15 Eagle 187

LANGLEY CONTRIBUTIONS TO THE F-15

The NASA Fighter Study Many of the basic design features of U.S. fighter aircraft have resulted from technology

pioneered at the Langley Research Center. Some examples are the area rule, the variable-sweep wing, wing maneuver flaps, and efficient afterbody-nozzle integration.

NASA continues to ensure that breakthrough concepts are quickly transferred to industry and DOD.

In 1967, Langley disseminated the results of in-house studies of a fighter configuration

known as LFAX-8, which incorporated several features that would later be evident in

the F-15 aircraft. Some of these features were

• Short propulsion package to minimize weight

• Engines placed forward for balance

• Horizontal ramp engine inlets for good performance at high angles of attack

• Horizontal tails located far aft on booms for increased stability and control

• Tailored twin-engine aft-end spacing and interfairing for efficient subsonic cruise 

conditions

Many industry design teams studied the database provided by Langley and these features were incorporated into many high-performance aircraft designs.

In 1968, the Department of Defense (DOD) requested that NASA respond to the F-15

request for proposals (RFP) in a manner similar to the industry contractors. The key person behind the NASA participation was Dr. John Foster, Director of the Defense Department Research and Engineering organization. He requested the participation for two

reasons. First, Foster felt that NASA’s aircraft designs for the F-15 mission would

embody advanced technology and serve as the upper limit of technology for industry

proposals. Second, NASA and its problem-solving expertise could minimize risks and

problems later in the development program.

Fighter concepts developed by NASA for the F-15 mission requirements.

LFAX-4

LFAX-9

LFAX-8

LFAX-10
Langley Contributions to the F-15

188 McDonnell Douglas F-15 Eagle

In response to Foster’s request, NASA organized a design team of about 70 professionals from the Langley, Ames, Glenn, and Dryden Research Centers. The team was colocated at Langley under the leadership of Langley researcher William J. Alford, Jr.

Roy V. Harris, Jr. and A. Warner Robins of Langley were members of a subteam responsible for configuration design and many other Langley researchers served on other subteams. The team spent about 4 months at Langley developing several fighter concepts

directed at the F-15 mission requirements. The breadth of studies included analytical

and wind-tunnel tests for the most promising configurations. Four fighter concepts were

studied in great detail:

• LFAX-4—a variable-sweep configuration

• LFAX-8— a fixed-sweep version of LFAX-4

• LFAX-9—wing-mounted twin-engine configuration

• LFAX-10—similar in external shape to Soviet MiG-25 Foxbat

Industry design teams visited Langley during the efforts and were continually updated

on the advantages, disadvantages, and technical maturity of the configurations. The

NASA team also briefed high ranking DOD officials. The LFAX-4 and LFAX-8 embodied features that would subsequently be evident in the McDonnell Douglas F-15 and

Northrop Grumman F-14 aircraft.

McDonnell Douglas was especially interested in the NASA fighter study as an

extremely valuable adjunct to the company’s design effort on the F-15. The LFAX-8

design made an indelible impression on the McDonnell Douglas design team, which

embraced the fundamental layout of the NASA configuration. The cranked-wing design

of the LFAX-8 had to be modified by McDonnell Douglas as the requirements for transonic maneuvering became more important. Another modification to the LFAX-8

involved the installation of a larger radar dish in the nose than the NASA team had

allowed for in their design. The installation required a larger diameter nose cone, and

although the NASA researchers deplored the increased supersonic drag caused by the

larger nose, the final design incorporated the larger dish.

F-15 Source Selection Following the NASA fighter study, 41 of the 70 NASA researchers became participants

in the detailed evaluation of the industry proposals by McDonnell Douglas, Fairchild,

and North American Rockwell. The studies and evaluation efforts, as well as developmental efforts at Langley, required over 6,000 hr in Langley facilities including the

Unitary Plan Wind Tunnel, the 4- by 4-Foot Supersonic Pressure Tunnel, the 7- by

10-Foot High-Speed Tunnel, the 16-Foot Transonic Tunnel, the 16-Foot Transonic

Dynamics Tunnel, the 20-Foot Vertical Spin Tunnel, and the 30- by 60-Foot (Full-Scale)

Tunnel. During the development of the F-15, Langley personnel acted as consultants to

the Air Force, and Langley provided a permanent member to the F-15 Program Office in

Dayton, Ohio for improved liaison and communications.

Following the award of the F-15 contract by the Air Force to McDonnell Douglas in

December 1969, Langley supported the development of the aircraft in several key areas.

Aerodynamic and Propulsion 

Integration Studies

Previous experiences with the F-111 and other advanced fighter concepts indicated that

an extremely large portion of the subsonic cruise drag of modern twin-engine fighters

is contributed by the aft end of the configuration (approaches 50 percent for some

configurations). Langley researchers learned that careful tailoring of the engine interfairings and tail surfaces could prevent excessive aft-end drag. In the course of F-111
Langley Contributions to the F-15

McDonnell Douglas F-15 Eagle 189

development, Langley researchers in the 16-Foot Transonic Tunnel under Blake W.

Corson, Jr. had developed test techniques and analysis methods to minimize this

problem.

A Langley team led by Bobby L. Berrier conducted extensive tunnel tests on a 4.7-scale

model of the F-15 for a critical assessment of aft-end drag on the baseline configuration,

which at the time had large ventral fins below the aft fuselage. Mutual adverse aerodynamic interference effects were evaluated for the aft-end components, including the

tails, tail booms, nozzles, and fuselage. After several tunnel entries, the Langley and

McDonnell Douglas research team recommended configuration changes that significantly reduced the subsonic cruise drag of the aircraft. Specifically, the ventral fins were

removed, the height of the vertical tails was increased to compensate for the resulting

loss of directional stability, and nozzle interfairings (between the nozzles and also

between the nozzles and tail booms) were added. Following briefings by Berrier to Air

Force and DOD managers (including Dr. John Foster, Director of Defense Research and

Engineering, and Robert Seamens, Secretary of the Air Force) of the test results and recommendations, the modifications (except for variable interfairings) were accepted for

all production aircraft. The variable interfairings were actually built for flight-test evaluations, but were never flown after it was learned that the modified production aircraft

met all critical mission requirements without the interfairing modification.

Upon completion of the drag clean-up studies, Berrier’s team also provided the subsonic, transonic, and supersonic aerodynamic data package for the production aircraft.

These data were obtained during multiple entries in the 16-Foot Transonic Tunnel

and the 4- by 4-Foot Supersonic Pressure Tunnel. The final aerodynamic data package

delivered by Langley included wind tunnel sting and distortion corrections and jet

exhaust correction increments. Performance predictions of the final production aircraft

were based on this data package.

Aft-end configurations of F-15 models before (top) and after (bottom) Langley modifications

such as removal of ventral fins, taller vertical tails, and nozzle interfairing.
Langley Contributions to the F-15

190 McDonnell Douglas F-15 Eagle

In addition to studies of the production F-15, the Langley team conducted exploratory

tests of the performance benefits of two-dimensional (2-D) nozzles and other advanced

propulsion integration concepts. These research studies provided the largest U.S. database for advanced nozzle integration and served as a valuable foundation for development of the 2-D thrust-vectoring nozzles used by the F-15 short takeoff and landing and

maneuver technology demonstrator (STOL/MTD) aircraft and the F-22 fighter.

Langley personnel conducted two other significant propulsion integration studies on the

F-15. The first study was a wind tunnel to flight correlation of a highly instrumented

powered model in the 16-Foot Transonic Tunnel and flight tests conducted at Dryden

Flight Research Center. The second effort was a study of acoustically induced loads on

the F-15 nozzles in the 16-Foot Transonic Tunnel and the Langley Acoustic and

Dynamic Laboratory. The stimulus for this study, led by Langley researcher John M.

Seiner, was the in-flight loss of external nozzle leaves (“turkey feathers”) from operational F-15 aircraft as a result of structural fatigue. The cause and fix for this phenomena

was identified during the Langley studies, but an alternate approach, at the expense of

cruise drag, of simply removing the nozzle external leaves before they could fatigue and

fall off was adopted by the Air Force.

High-Angle-Of-Attack and 

Spin Research

The Air Force and the Navy had expressed notable dismay over the relatively poor and

unforgiving characteristics of the F-4 aircraft at high angles of attack. The F-4 exhibited

a sudden directional divergence (nose slice) and other control-induced characteristics at

high angles of attack that made the aircraft susceptible to loss of control and inadvertent

spins. The two services lost a combined total of over 100 F-4’s to accidents involving

these characteristics during the operational life of the aircraft. Understandably,

McDonnell Douglas approached the design of the F-15 with the intention of providing a

high level of stability and spin resistance for the new air superiority fighter.

Langley technician Ronald White with one of two F-15 drop

models used for research on spin-entry characteristics.
Langley Contributions to the F-15

McDonnell Douglas F-15 Eagle 191

William P. Gilbert and James S. Bowman, Jr. led Langley research on the high-angle-ofattack and spin characteristics of the F-15. Facilities used for the effort included the

Full-Scale Tunnel, the Spin Tunnel, and a helicopter-launched, radio-controlled drop

model. McDonnell Douglas had done considerable homework as a result of the F-4

experience, and entered the F-15 development program with an appreciation of the stability and control features required.

In addition to careful layout of the airframe for satisfactory high-angle-of-attack stability of the F-15, McDonnell Douglas adopted a unique control augmentation system

(CAS) in which movement of the control stick for lateral control resulted in deflections

of the rudders, rather than the ailerons, at high angles of attack. With this approach,

McDonnell Douglas restricted spin inducing aileron inputs while retaining adequate roll

response. Initial analyses of this control concept by Langley researchers indicated that it

would greatly enhance the spin resistance of the F-15. A demonstration of the spin resistance of the aircraft through the use of dynamically scaled free-flying models was still

required. In addition, Langley was requested to identify the potential spin and recovery

characteristics of the F-15 and the size of the parachute required for emergency spin

recovery for a flight-test aircraft.

Results of tests of a 1/30-scale model in the Spin Tunnel indicated that the F-15 would

exhibit developed spins if it exceeded the capability of the CAS to prevent spin entry.

However, the ability of the aircraft control surfaces to recover the F-15 from spins was

predicted to be very good. Meanwhile, tests in the Full-Scale Tunnel in 1971 on a

0.10-scale free-flying model and with a 0.13-scale model dropped from a helicopter

indicated that the F-15 would be very stable at high-angle-of-attack conditions and that

spin entry would be very difficult with the CAS active. Using the drop model, Langley

researchers led by Charles E. Libbey defined a very limited range of control inputs and

aircraft attitudes that enabled entry into a spin. In summary, the superior high-angle-ofattack behavior that had been anticipated by the McDonnell Douglas designers of the

F-15 was validated and vividly demonstrated by the Langley dynamic-model tests.

In 1972, the Dryden Research Center assessed the impact of model size and Reynolds

number on the results of the Langley tests. Dryden built and conducted drop tests with a

0.38-scale unpowered model, which was launched from a B-52. Results of the test program correlated well with the results obtained from the smaller model at Langley, and

further substantiated the spin resistance of the F-15 configuration.

Flutter Clearance Flutter clearance testing of the F-15 in the Langley 16-Foot Transonic Dynamics Tunnel

required four tunnel entries. The tests were conducted in 1971 and were led by Langley

researcher Moses G. Farmer. McDonnell Douglas provided a full-span F-15 model for

the initial tests in the facility. Unfortunately, the F-15 was among a class of modern

fighters that encountered tail flutter problems that were related to the pioneering use of

composite materials in high-performance aircraft. The tunnel tests indicated that the

original F-15 design would exhibit horizontal-tail flutter within its operational envelope.

The early detection of this potentially catastrophic deficiency was a valuable contribution of Langley to the program. With the Langley results in hand, McDonnell Douglas

engineers conducted flutter tests of the tail components in their own facilities. The problem was solved by redesigning the horizontal-tail geometry to control the aerodynamic

center and mass balancing of the tail surface. By removing part of the inboard leading

edge of the horizontal tail and adding additional balancing weight, McDonnell Douglas

was able to clear the envelope of flutter for the development program. McDonnell
Langley Contributions to the F-15

192 McDonnell Douglas F-15 Eagle

Douglas also removed a portion of wing near the wingtips to alleviate an objectionable

buffet characteristic at transonic maneuvering conditions; however, the requirements for

this modification came from flight-test evaluations.

The F-15 Short Takeoff and 

Landing and Maneuver 

Technology Demonstrator

In 1984, the Flight Dynamics Laboratory of the Air Force Aeronautical Systems Division awarded a contract to McDonnell Douglas for an advanced development STOL/

MTD experimental aircraft. The idea behind the program was to develop an aircraft that

could land and takeoff from sections of wet, bomb-damaged runway under bad weather

conditions and severe crosswinds without active ground-based navigational assistance.

The F-15 STOL/MTD aircraft was a direct adaptation of a configuration developed in

Langley sponsored programs conducted in the 1970’s. Government and industry studies

of nonaxisymmetric two-dimensional (2-D) nozzles in the early 1970’s had identified

significant payoffs for thrust-vectoring 2-D nozzle concepts. To better integrate the various 2-D nozzle technology programs and also to exchange data on this concept, a joint

NASA and DOD workshop was initiated and sponsored by Langley in September 1975.

To strengthen program integration and develop recommendations for further development of 2-D nozzles, an ad hoc interagency nonaxisymmetric nozzle working group was

formed at the workshop. Langley researcher Bobby Berrier was appointed as the NASA

representative to this group, which also included a member from the Air Force, the

Navy, and the Defense Advanced Research Projects Agency (DARPA) organizations.

The group advocated for a flight research program on the thrust-vectoring 2-D nozzle

concept.

The working group provided reviews and progress reports to senior management officials throughout the mid-1970’s to early 1980’s. The working group advocated for studies on three potential flight research vehicles. To avoid duplication, the Air Force

studied the F-111 vehicle, the Navy studied the YF-17/F-18 vehicle, and Langley studied the F-15 vehicle. In 1977, Langley initiated a system integration study of thrust-vectoring, thrust-reversing, 2-D nozzles on the F-15 with McDonnell Douglas. A

Langley researcher Moses Farmer with F-15 model in preparation

for flutter tests in the 16-Foot Transonic Dynamics Tunnel.
Langley Contributions to the F-15

McDonnell Douglas F-15 Eagle 193

companion study of 2-D nozzle integration with the engine was initiated with Pratt and

Whitney by the Glenn Research Center. The eventual F-15 STOL/MTD aircraft with

thrust-vectoring, thrust-reversing, 2-D nozzles and a canard for trim of thrust-vectoring

forces is a direct descendent of the configuration developed in these studies funded by

NASA. In addition, multiple tests for both the F-15 generic and the F-15 STOL/MTD

were conducted at the Langley 16-Foot Transonic Tunnel to study propulsion integration and power effect of thrust-vectoring, in-flight thrust-reversing (including methods

for trim), 2-D nozzles on the F-15. As a result of its key role in developing the technology, Langley provided nearly all the features of the F-15 STOL/MTD aircraft.

The 16-Foot Transonic Tunnel team, led by Bobby Berrier, Francis J. Capone,

Richard J. Re, Odis C. Pendergraft, Jr., Mary L. Mason, Laurence D. Leavitt, and others

developed during the 1980’s the most extensive design database in the world for low

observable, thrust-vectoring, thrust-reversing (yaw and pitch), 2-D nozzles.

In recognition of Langley’s leadership role in thrust-vectoring technology, the Air Force

and McDonnell Douglas consulted frequently with the Langley staff, particularly with

the propulsion integration experts under William P. Henderson at the 16-Foot Transonic

Tunnel and the flight dynamics experts at the Full-Scale Tunnel. Free-flight tests conducted by Joseph L. Johnson, Jr.’s group in the Full-Scale Tunnel demonstrated that the

aircraft would have excellent handling characteristics at high angles of attack. The most

impressive research results in flight dynamics, however, occurred when the Langley

researchers equipped the free-flight model with special 2-D nozzles that provided thrust

vectoring in yaw as well as pitch. The superior control provided by the multiaxis vectoring was demonstrated when the model was easily flown at angles of attack up to about

85 deg without vertical-tail surfaces.

The first flight with the thrust-vectoring nozzles took place on May 16, 1989. The aircraft was transferred to Edwards Air Force Base for joint flight tests by the Air Force

and McDonnell Douglas. The 2-D nozzles were first tested in flight on March 23, 1990.

Test flights demonstrated a 25-percent reduction in takeoff roll, and the thrust-reversing

feature made it possible for the F-15 to land on just 1,650 ft of runway (7,500 ft is

The F-15 STOL/MTD flying with canards and thrust-vectoring nozzles.
Langley Contributions to the F-15

194 McDonnell Douglas F-15 Eagle

required for the standard F-15). In addition, thrust reversal was used during up-andaway flight to produce rapid decelerations—a useful feature for close-in air-to-air combat. During the flight program, the F-15 STOL/MTD made vectored takeoffs with rotation demonstrated at speeds as low as 42 mph. The program ended on August 15, 1991,

after accomplishing all of the flight objectives. 
Highlights of Research by Langley for Missiles

Missiles 195

Missiles

HIGHLIGHTS OF RESEARCH BY LANGLEY FOR MISSILES

1. From the 1950’s Langley has worked to improve aerodynamic performance and roll

characteristics of the Sidewinder missile, which resulted in rollerons on the tail fin.

2. Langley wind-tunnel studies assessed the effects of mounting Sidewinders on

wingtips and pylons on fighter aircraft stability and maneuverability.

3. Langley participated in the development of the Sparrow missile in the early 1950’s

with flight tests to improve booster performance and supersonic wind-tunnel studies

that resulted in changes to the nose and fin design.

4. Langley determined Sparrow missile carriage and separation loads for several

aircraft.

5. Langley studied of the aerodynamics and relative drag of certain carriage configurations of the Advanced Medium Range Air-to-Air Missile.

6. Langley provided aerodynamic data from wind-tunnel tests during development of

the Patriot missile.

7. Langley helped improve the stability problems of the early Hawk missile by proposing cutouts in the wings.

8. At the request of the Department of Defense, Langley assesses the impact of missiles

and external stores on aircraft performance, spin recovery, and flutter.
Highlights of Research by Langley for Missiles

196 Missiles

As a result of unique supersonic wind tunnels and broad expertise across several technical disciplines, the NASA Langley Research Center has conducted extensive fundamental and applied research on missile configurations. Langley also conducts investigations

to define the characteristics of specific missiles when requested by the Department of

Defense (DOD). Langley typically addresses the aerodynamic performance, stability,

and control characteristics of missile configurations; the aerodynamic phenomena associated with the carriage and release of missile shapes; and the effects of missiles and

other external stores on the performance, stability and control, spin recovery, and

aeroelasticity characteristics of the aircraft. Contributions have included the analysis

and enhancement of missile shapes, the development and validation of advanced computational methods for missiles, and the development of unique wind-tunnel techniques

for efficient and insightful tests. Langley has contributed to missile configurations for

over 45 years in partnership with DOD and industry. These contributions are continuing

for programs such as the Sidewinder, Sparrow, Advanced Medium Range Air-to-Air

Missile (AMRAAM), Hawk, and Patriot missiles.

Langley facilities that supported research on advanced missile configurations included

the 4- by 4-Foot Supersonic Pressure Tunnel, the Unitary Plan Wind Tunnel, the 16-Foot

Transonic Tunnel, the 8-Foot Transonic Pressure Tunnel, and the Mach 6 High

Reynolds Number Tunnel. Langley researchers also utilized the facilities at the NASA

Wallops Flight Facility for missile testing.
Langley Contributions to Missiles

Missiles 197

LANGLEY CONTRIBUTIONS TO MISSILES

Background In support of the Department of Defense (DOD), Langley Research Center is frequently

requested to assist in the assessment and development of missiles. Langley provides

support in the areas of aerodynamics, stability, and control for the isolated missile configuration, as well as in areas that might be affected by the carriage and release of the

missile (aircraft performance, spin recovery, and flutter).

Langley became involved in the development of missile systems in the early 1950’s,

when a detachment of Langley researchers formed the core of what would become the

NASA Wallops Flight Facility. These pioneering researchers used booster rockets to

assess the aerodynamic characteristics of evolving air-to-air military missiles.

When large-scale supersonic wind tunnels were put into operation at Langley, special

tests and test techniques were developed and validated for basic research for specific

missile programs. Langley’s leader in these early efforts was M. Leroy Spearman, who

maintained a close working relationship with DOD and other agencies. In the 1960’s

and 1970’s, Charles M. Jackson and Wallace C. Sawyer led the Langley missile program, which focused on a number of technical issues that were within the interests of

the NASA program. The program included an expansion of the database for missile

design (led by Jerry M. Allen and Adolphus B. Blair, Jr.), the development and validation of computational codes for missile aerodynamics (led by David S. Miller and Richard M. Wood), store carriage and separation (led by Robert L. Stallings, Jr.), and

experimental techniques (led by William Corlett).

The vast majority of work in the Langley missile program involved research on representative missile shapes; however, very significant contributions were made to specific

missile programs.

AIM-9 Sidewinder In 1953, the Naval Ordnance Test Section requested assistance from Langley in the

development of a short range, guided air-to-air missile for close-in combat. Known as

the Sidewinder, the missile was to be heat seeking—that is, able to lock on to a target’s

heat producing sources, and featured forward canards for improved control.

At Wallops Island, Langley researchers conducted flight tests to improve the roll characteristics at supersonic speeds of the Sidewinder. During the tests, the missile was

mounted atop a rocket test section. Langley developed special dampers, known as rollerons, for the rear control surfaces of the missile, which eliminated undesirable oscillatory roll tendencies. In 1956, Langley researchers studied how fighter aircraft would

perform at supersonic speeds with various numbers of Sidewinder missiles stored in

underwing locations and wingtip hard points. These studies were conducted in the

Langley 4- by 4-Foot Supersonic Pressure Tunnel. The tests helped to establish limits on

the external store capability of aircraft destined to carry the missile.

Through the years, programs have improved the maneuverability and range of the

Sidewinder missile, and Langley has conducted numerous wind-tunnel test programs in

the Langley Unitary Plan Wind Tunnel in cooperation with the Naval Weapons Center,

China Lake, California. The most recent efforts in 1990, led by Blair and Allen, were
Langley Contributions to Missiles

198 Missiles

conducted in the Unitary Plan Wind Tunnel and focused on the potential benefits of

reduced tail span for enhanced supersonic maneuverability. The Langley and Navy team

also examined a long range Sidewinder configuration, which incorporated an increased

body diameter for more booster fuel.

Air Force crew loads a Sidewinder.

Sidewinder missile research model in the Langley Unitary Plan Tunnel.
Langley Contributions to Missiles

Missiles 199

AIM-7 Sparrow In August 1948, Langley assisted the Navy and its contractors, the Sperry Corporation

and the Douglas Corporation, in the development of the nation’s first medium range

guided air-to-air missile system. Langley constructed two uninstrumented development

models of the missile, the XAAM-N-2 Sparrow I. The models were flown at the rocket

range at Wallops to solve early booster problems. Refinements to the nose and fin sections of the missile were completed through subsonic and supersonic tests in Langley

wind tunnels during the early 1950’s.

Once the aerodynamics of the Sparrow configuration had been proven, the launching

characteristics from positions under the wings, on the wingtips, and under the fuselage

of the aircraft had to be determined for factors that might hinder aircraft and missile performance. With scale models, realistic simulations of missile launches were conducted

during the mid-1950’s in the Langley 7- by 10-Foot High-Speed Tunnel. Various fighter

designs with the missiles carried externally (including the F-4) were tested at supersonic

speeds in the Langley Unitary Plan Wind Tunnel to determine the aerodynamic loads on

the missiles, as well as other external stores. Reliable and extremely accurate, the

Sparrow later became the medium range workhorse for the Navy and Air Force.

Updates of the Sparrow missile system, such as the Sparrow III, also were tested in Langley wind tunnels. Initial tests of the advanced version began with an examination of the

aerodynamic characteristics of the missile at supersonic speeds in the Unitary Plan

Wind Tunnel in 1977. During the early to mid-1980’s, further studies of the separation

characteristics from simulated aircraft were conducted again in the Unitary Plan Wind

Tunnel at speeds in excess of a Mach number of 2.

AIM-120 AMRAAM By the mid-1980’s, the military hoped to gradually replace the air-to-air medium range

guided missile mainstay, the AIM-7 Sparrow with a more advanced weapons delivery

system that would be carried by the next generation of fighters with supersonic cruise

capability. The new missile, produced by McDonnell Douglas was designated the

AIM-120 Advanced Medium Range Air-to-Air Missile (AMRAAM).

Initial aerodynamic studies of the AMRAAM at Langley focused on the missile itself,

with scale models studied on a weapons palette. Extensive studies were conducted at

supersonic speeds in the Langley Unitary Plan Wind Tunnel, first on a generic wingbody configuration and later on an advanced fighter configuration to determine the optimum external carriage locations. Researchers examined such factors as the amount of

drag produced by missile arrangements and the amount of space required between missiles for effective weapons launch.

Today, the AMRAAM dominates the active radar missile field. Export orders for the

AMRAAM totaled more than 7000, which is more than ten times the orders of its competitors combined.

Impact on Aircraft 

Characteristics

Since Langley is usually requested to support the development of high-performance aircraft, the Center is in an excellent position to assess the impact of missiles and other

external stores on characteristics of the aircraft. Thus, assessments of the impact of missile configurations are normally included in performance evaluations in transonic and

supersonic wind tunnels, studies of spin recovery characteristics in the Langley 20-Foot

Vertical Spin Tunnel, and flutter clearance tests in Langley 16-Foot Transonic Dynamics

Tunnel.

Highlights of Research by Langley for the B-2

Northrop Grumman B-2 Spirit 201

Northrop Grumman B-2 Spirit

HIGHLIGHTS OF RESEARCH BY LANGLEY FOR THE B-2

1. At the request of the Air Force, Langley specialists participated as members of B-2

technical review teams during design and early development stages.

2. Langley provided critical wind-tunnel tests with multiple entries in 5 Langley tunnels during the development program.

3. Areas addressed in the Langley tests included propulsion integration, high-angle-ofattack and low-speed stability and control, cruise performance, and spinning.

SPECIFICATIONS

Manufacturer

Northrop Grumman

Date in service

December 17, 1993

Number built

21 on order through year 2000

Type

Multirole bomber

Crew

Two (provisions for third)

Engine

General Electric F118-GE-100 

nonafterburning turbofan

USER

U.S. Air Force

DIMENSIONS

Length . . . . . . . . . . . . . . 69.0 ft

Height . . . . . . . . . . . . . . 17.0 ft

Wing area. . . . . . . . . 5,140 sq ft

WEIGHT

Empty . . . . . . . . . . . 153,700 lb

Weapon load . . . . . . . 40,000 lb

Max takeoff . . . . . . . 376,000 lb

PERFORMANCE

Speed . . . . . . . . . high subsonic

Range. . . . . . . . . . . . 6,000 n mi
Highlights of Research by Langley for the B-2

202 Northrop Grumman B-2 Spirit

The B-2 Spirit’s low observable, or stealth, characteristics give it the unique ability to

penetrate an enemy’s most sophisticated defenses and threaten its most valued, and

heavily defended, targets. Northrop Grumman successfully met enormous technical

challenges in blending the features and concepts required for low observability with the

features required for high aerodynamic efficiency and large payload. In recognition of

the significant accomplishments in the development of the B-2, Northrop Grumman was

awarded the Collier Trophy in 1991. The NASA Langley Research Center provided key

information for the design and development process by Northrop Grumman.

Some of the more obvious B-2 design challenges are apparent, including the efficient

operation of highly integrated engine inlets; providing satisfactory stability, control, and

handling characteristics for a flying-wing configuration without tail surfaces; and meeting mission performance specifications with high aerodynamic efficiency.

At the request of the Air Force, Langley researchers participated in preproduction technical reviews of the B-2 and later provided tests in several unique facilities at Langley

during the development process. Langley facilities used for B-2 tests included the

National Transonic Facility (NTF), the16-Foot Transonic Tunnel, the 16-Foot Transonic

Dynamics Tunnel, the 30- by 60-Foot (Full-Scale) Tunnel, and the 20-Foot Vertical Spin

Tunnel.
Langley Contributions to the B-2

Northrop Grumman B-2 Spirit 203

LANGLEY CONTRIBUTIONS TO THE B-2

NASA supported Northrop Grumman in the aerodynamic design and development of

the B-2 for over 15 years. Some of the more critical configuration development tests

included the B-2 planform, the shielded upper-surface engine inlets, and the flight control system. At times, this effort approached 20 percent of the test operational schedule

for some facilitates.

B-2 model during tests in the National Transonic Facility (NTF) at Langley.

Free-spin and spin recovery tests of the B-2 in the Langley Spin Tunnel.

Highlights of Research by Langley for the B-1B

Rockwell B-1B Lancer 205

Rockwell B-1B Lancer

HIGHLIGHTS OF RESEARCH BY LANGLEY FOR THE B-1B

1. At the request of the Air Force, Langley participated in early studies and assessments of configurations that led to the B-1A and B-1B, including the Advanced

Manned Strategic Aircraft (AMSA) Program.

2. The B-1 utilizes the variable-sweep wing concept that was matured by Langley.

3. Langley assessments of the high-angle-of-attack stability and control characteristics

of the B-1A identified an undesirable longitudinal instability (pitch-up) that was

eliminated by modifications to the flight control system.

4. Langley conducted several investigations of aft-end propulsion integration and the

application of supercritical wing aerodynamics to reduce the cruise drag of the

B-1A.

5. At the request of the Air Force, Langley conducted diagnostic wind-tunnel tests to

analyze high loads on the engine nozzle flaps for the B-1B.

6. Flutter clearance tests and analysis of a unique wing oscillation problem were conducted at Langley.

SPECIFICATIONS

Manufacturer

North American Aircraft of 

Rockwell International

Date in service

B-1B . . . June 1985

Type

Bomber

Crew

Four

Engine

General Electric F101-GE-102 

with afterburner

USER

U.S. Air Force

DIMENSIONS

Wingspan. . . . . . . . . . . 137.2 ft

Length . . . . . . . . . . . . . 145.8 ft

Height . . . . . . . . . . . . . . 33.6 ft

Wing area. . . . . . . . . 1,946 sq ft

WEIGHT

Empty . . . . . . . . . . . 186,234 lb

Gross . . . . . . . . . . . . 477,000 lb

PERFORMANCE

Max speed . . . . . Mach number

of 1.2

Range. . . . . . . Intercontinental,

unrefueled
Highlights of Research by Langley for the B-1B

206 Rockwell B-1B Lancer

The Rockwell (now Boeing) B-1B is a multirole, long range bomber, capable of flying

intercontinental missions without refueling, then penetrating sophisticated enemy

defenses. The B-1B’s electronic jamming equipment, infrared countermeasures, radar

location, and warning systems complement its low radar cross section and form an integrated defense system for the aircraft. Rockwell was awarded the Collier Trophy in

1976 in recognition of accomplishments for the B-1 development program.

Langley’s association with the B-1 began with Air Force requests for active NASA

involvement in several Air Force studies for advanced manned strategic bombers in the

mid-1960’s. Langley’s involvement in advanced supersonic transports significantly

enhanced the technical capabilities of the Air Force and Rockwell. As the B-1A Program progressed, the Langley staff conducted extensive tests and analysis of cruise-drag

reduction, high-angle-of-attack behavior, and flutter. Following the cancellation of the

B-1A Program and the initiation of the B-1B Program, Langley contributed to a joint

NASA, DOD, and industry flight and wind-tunnel study to determine the cause of

extremely high loads on the engine nozzle flaps for the B-1B aircraft.

Langley facilities involved in support for the B-1A and B-1B Programs included the

Langley 30- by 60-Foot (Full-Scale) Tunnel, the 16-Foot Transonic Tunnel, the 8-Foot

Transonic Pressure Tunnel, the 16-Foot Transonic Dynamics Tunnel, the 20-Foot Vertical Spin Tunnel, piloted simulators, and radio-controlled drop models.
Langley Contributions to the B-1B

Rockwell B-1B Lancer 207

LANGLEY CONTRIBUTIONS TO THE B-1B

Early Strategic Bomber 

Studies

Activities that led to the development of the B-1B bomber began in 1961, when the Air

Force initiated studies under the Subsonic Low Altitude Bomber (SLAB) Program. The

mission requirements and name of the bomber program continued to change during the

early 1960’s and became the Advanced Manned Strategic Aircraft (AMSA) Program in

1965. NASA’s contributions in the definition of the FX Advanced Tactical Fighter

(F-15) Program had not gone unnoticed by Air Force leaders involved in the AMSA

Program. The close working relationships and mutual respect that existed between the

Air Force and NASA are exemplified in excerpts from letters of request from the Air

Force to NASA Headquarters for NASA participation in the AMSA effort.

From Lieutenant General Holzapple (Deputy Chief of Staff, Research and Development) to Dr. Mac Adams (NASA Associate Administrator for Advanced Research and

Technology) on March 27, 1968:

It appears appropriate to have an independent review of the technical status

of the (AMSA) air vehicle/engine configurations that have evolved. Informal

discussions with Mr. Mark Nichols of NASA Langley indicate that NASA may

be able to make a significant contribution in the form of evaluation and constructive criticism. Specifically, we have in mind verification of the latest preliminary designs and associated performance calculations and wind-tunnel

results to ensure that our optimism is justified. In addition, such activity by

NASA at this time would provide the appropriate background for NASA participation in any contractor source selection that might eventually come to

pass.

From General McConnell (Air Force Chief of Staff) to Mr. James Webb (NASA Administrator) on June 13, 1968:

The continued technical support that NASA has provided the Air Force in

defining the FX Advanced Tactical Fighter has been most useful. I feel that

our cooperative efforts have resulted in a very positive gain for the Air

Force... Because of the value we place in NASA’s expertise I would also ask

you to consider supporting our AMSA effort. This should serve not only to

improve our product but also to increase the confidence of others in our work.

In response to these requests, Langley participated extensively in AMSA reviews, planning discussions, and exploratory wind-tunnel tests of candidate configurations. The

expertise of the Langley staff in supersonic aerodynamics, and their active participation

in the U.S. Supersonic Transport Program were especially valuable to the AMSA Team.

The evolving requirements for the AMSA included challenging mission capabilities at

supersonic speeds and low altitudes. As the studies began, it became obvious that application of the variable-sweep wing concept developed at Langley to the candidate

bomber configurations was extremely beneficial.
The B-1A Program

208 Rockwell B-1B Lancer

THE B-1A PROGRAM

In June 1970, the Air Force awarded development contracts to North American

Rockwell to build the B-1A bomber airframe and to the General Electric Corporation to

provide the engines for the advanced bomber. Four B-1A prototypes were ordered for

the development program. Langley immediately received a request from the Air Force

to assist in the assessment and development of the B-1A.

High-Angle-of-Attack 

Research

The Air Force requested that Langley conduct the complete suite of tests for highperformance military aircraft, including wind-tunnel free-flight model tests, spin tests,

and radio-controlled drop-model tests. Rockwell engineers were interested in the potential variation of handling characteristics with wing-sweep position and were anxious to

uncover any problems, along with the solutions.

Free-flight model tests of the B-1A were conducted in the Langley 30- by 60-Foot (FullScale) Tunnel in 1972, by Langley researchers William A. Newsom, Jr. and Sue B.

Grafton. Preliminary wind-tunnel tests of the model indicated that a severe longitudinal

instability (pitch-up) would be encountered for angles of attack immediately above wing

stall. This undesirable result was attributable to the relatively high position of the horizontal tail, which placed it in an adverse flow field at post-stall angles of attack. Subsequently, Langley radio-controlled drop-model tests by Charles E. Libbey vividly

demonstrated the undesirable pitch-up characteristic. Piloted simulator studies were

Langley researcher William Newsom with the B-1A free-flight model.
The B-1A Program

Rockwell B-1B Lancer 209

B-1A model in free-flight tests in the Langley Full-Scale Tunnel in 1972.

B-1A drop model being prepared for helicopter drop test in 1974.
The B-1A Program

210 Rockwell B-1B Lancer

conducted at Langley by William D. Grantham and Langley pilot Perry L. Deal to evaluate the stall recovery characteristics of the B-1A under simulated mission conditions,

such as hook-up and disengagement during air-to-air refueling. Grantham and his team

of Langley and Air Force research pilots found that recovery from the pitch-up was very

demanding and that a high potential for inadvertent secondary stalls (and pitch-ups)

existed for the basic aircraft. The Langley, Rockwell, and Air Force team evaluated several control system concepts to artificially limit the angle of attack of the B-1A and

thereby eliminate the post-stall instability from the operational envelope. Based in part

on the Langley studies, an angle-of-attack limiter was subsequently incorporated into

the B-1A flight control system.

Free-spin tests of a B-1A model were conducted in the Langley 20-Foot Vertical Spin

Tunnel by James S. Bowman, Jr.; however, the angle-of-attack limiter system precluded

serious concern of inadvertent spins with the B-1A.

Cruise Drag At the request of the Air Force, Langley researchers analyzed and measured the cruisedrag characteristics of the B-1A during the design process and the development

program.

At the request of the Air Force, Langley researchers William P. Henderson and Bobby

L. Berrier participated in a special B-1A drag audit in the summer of 1972. The audit,

which was requested by the B-1 Systems Program Office (SPO), consisted of a detailed

assessment of the external and internal drag and installed thrust of the B-1A to evaluate

the progress of the program and identify any high risk areas. The audit team consisted of

12 members from the Air Force and NASA.

Drag reduction studies for the B-1A were also conducted in the Langley 8-Foot Transonic Pressure Tunnel under the leadership of Theodore G. Ayers. The studies were

directed at two objectives: the reduction of aerodynamic drag caused by the relatively

large over-wing fairing and the potential application of supercritical wing aerodynamics. A cooperative Langley and Rockwell investigation of supercritical aerodynamics

promised significant results; however, the Air Force directed Rockwell to turn their

design information over to General Dynamics for possible application to the FB-111,

and the B-1A application was not revisited.

B-1A model in the Langley 16-Foot Transonic Tunnel.
The B-1A Program

Rockwell B-1B Lancer 211

Aircraft such as the B-1B that incorporate advanced configuration features such as

variable-sweep wing and variable nozzle throat and exit areas for engines have detailed

configuration features that can result in excessive drag at cruise conditions. For example, variable-sweep wings can have steps and gaps in the wing and glove juncture that

can produce high drag. Variable exhaust nozzles when closed down to cruise settings

often have large boat tail angles that result in high drag. Also, for twin-engine configurations with closely spaced exhaust nozzles, the large surface slopes in the gutter between

the nozzles can cause flow separation and high drag.

To improve the drag characteristics of the B-1A, an investigation of several modifications on a 0.06-scale model was conducted in 1974 in the Langley 16-Foot Transonic

Tunnel. Langley researchers Richard J. Re and David E. Reubush, with Rockwell and

Air Force participants conducted tests to determine the effects of nozzle configuration,

wing and glove fairings, fuselage underfairings, and other configuration modifications.

Flutter The B-1A configuration underwent tests in the Langley 16-Foot Transonic Dynamics

Tunnel (TDT) during several entries to determine flutter characteristics of the tail surfaces, obtain flutter clearance for the complete configuration, and investigate a unique

outer wing oscillation phenomenon. Langley researchers Charles L. Ruhlin and

Moses G. Farmer led these tests, which began in late 1972. Flutter clearance for the

B-1A was obtained during this test program, and flight tests of the aircraft proceeded.

During the flight tests at high altitude maneuvering conditions, an unusual aeroelastic

phenomenon was encountered in which the outer wings of the aircraft exhibited a relatively low frequency, low amplitude undamped oscillation for certain values of wing

sweep and flight conditions. Several entries in the TDT were conducted from 1973 to

1987 to further analyze the driving mechanism, which was identified as periodic shockinduced separation. The oscillations occurred near critical Mach number conditions for

the wing airfoil and only at high positive angles of attack. The instability was demonstrated in the wind tunnel, however, at slightly different conditions than in flight.

On June 30 1977, President Jimmy Carter announced that the United States would not

proceed with the production of the B-1A bomber. However, flight tests of the four B-1A

prototype aircraft continued until April 1981.

B-1A flutter model mounted in the Langley 16-Foot Transonic Dynamics Tunnel.
The B-1B Program

212 Rockwell B-1B Lancer

THE B-1B PROGRAM

As the B-1A Program was terminated, the DOD initiated a study through the Air Force

Scientific Advisory Board to determine the need and direction for future strategic bombers. The results of the study concluded that a derivative of the B-1A, the B-1B, was the

best candidate to fulfill the nation’s needs within the envisioned mission requirements

and the projected deployment date. Although the B-1B retained the same general geometrical shape of the B-1A, the shift in emphasis on penetration of highly defended targets resulted in modifications to the more crucial aircraft systems, especially defensive

systems. The B-1B has a maximum speed of only half that of the B-1A, but it incorporates many more advanced concepts for enhanced survivability. Then known as the

Long Range Combat Aircraft (LRCA), the B-1B was selected as the next strategic

bomber and endorsed for production by President Ronald Reagan in October 1981.

Dynamic Loads on Engine 

Nozzle Flaps

The B-1B experienced excessive dynamic loads on the engine external nozzle flaps,

which led to premature failures of the flap attachment system. In 1987, a joint Langley,

Rockwell, and Air Force wind-tunnel and full-scale flight investigation of dynamic

loads on engine nozzle flaps was conducted. A 0.06-percent full-span model of the B-1B

with powered engine nacelles was tested in the Langley 16-Foot Transonic Tunnel under

the leadership of Langley researchers John M. Seiner, Francis J. Capone, and Odis C.

Pendergraft, Jr. The Langley researchers had previously participated in similar dynamic

loads tests for the F-15. (See Langley Contributions to the F-15.) Seiner had led analysis

of the principal mechanisms responsible for high loads on the external flaps that are

caused by twin-plume supersonic resonance phenomena. The results of the B-1B study

were similar to the previous F-15 analysis and contributed further understanding for

improved design and analysis methods. Although the study team identified several solutions to the dynamic loads problem, the Air Force eventually decided to fix the problem

by permanently removing the external flaps from the nozzles, which increased cruise

drag, but reduced weight. 

B-1B model in an inverted position for nozzle flap

load investigation in the Langley 16-Foot Transonic Tunnel.
Highlights of Research by Langley for the X-31

Rockwell-MBB X-31 213

Rockwell-MBB X-31

HIGHLIGHTS OF RESEARCH BY LANGLEY FOR THE X-31

1. Langley contributed to exploratory studies of a fighter configuration designed to

exploit high angles of attack in a precursor to the X-31 Program with Rockwell.

2. Working with Rockwell, Langley identified unacceptable characteristics of the initial

design and successfully revised the configuration.

3. At the request of the Defense Advanced Research Projects Agency, Langley participated in the International X-31 Program and provided information on stability and

control, control system effects, configuration effects, thrust-vectoring system, spin

recovery, and recovery from out of control conditions.

4. During flight tests of the two X-31 research aircraft at NASA Dryden Flight

Research Center, Langley provided facility support and technical consultation and

analysis.

5. On two occasions, Langley provided timely solutions to critical X-31 deficiencies

that had stopped the flight program.

SPECIFICATIONS

Manufacturer

Rockwell

First Flight

October 1990

Type

Experimental demonstrator 

of combat utility of flight at 

extreme angles of attack

Crew

One

Engine

General Electric F404-GE400

USERS

NASA (Langley and Dryden), 

Rockwell, DARPA, U.S. Navy, 

Deutshe Aerospace-MBB, and 

German Ministry of Defense

DIMENSIONS

Wingspan. . . . . . . . . . . . 23.8 ft

Length . . . . . . . . . . . . . . 48.8 ft

Height . . . . . . . . . . . . . . 14.6 ft

Wing area. . . . . . . . . . .226 sq ft

WEIGHT

Takeoff. . . . . . . . . . . . 16,100 lb

PERFORMANCE

Max speed . . . . . Mach number

of 1.28
Highlights of Research by Langley for the X-31

214 Rockwell-MBB X-31

The Rockwell (now Boeing) and Messerschmitt-Bolkow-Blohm (MBB) X-31

Enhanced Fighter Maneuverability (EFM) Demonstrator was designed to demonstrate

the effectiveness of controlled maneuvers at extreme angles of attack during certain

close-in air combat scenarios. The first International (U.S. and Federal Republic of

(West) Germany) X-Plane Program showed the value of using thrust vectoring (redirecting engine exhaust flow) with advanced flight control systems to provide unprecedented

levels of controlled flight to very high angles of attack. Whereas many previous fighters

experienced loss of control in this regime, the X-31 was able to maneuver without fear

of loss of control or inadvertent spins, which provided the pilot with new tactical

options. The X-31, along with the NASA F-18 High Alpha Research Vehicle, was used

in extensive flight tests at NASA Dryden Flight Research Center in the 1990’s to provide the technologies and tactical evaluations to remove the high-angle-of-attack

“barrier.”

Langley became involved in the X-31 Program in 1984 in a cooperative research program with Rockwell to develop a fighter configuration capable of highly agile flight at

extreme angles of attack. Free-flight model tests at Langley led to a major redesign of

the Rockwell candidate configuration. When Rockwell, the Defense Advanced Research

Projects Agency (DARPA), and the West Germans formed the X-31 Program, the staff

at Langley was requested to participate in the configuration development. Langley

researchers conducted extensive studies of the stability, control, and thrust-vectoring

system of the vehicle. Langley remained active in the program as Dryden became the

responsible test organization during the flight tests of two X-31 demonstrator aircraft.

Flight tests began at Dryden in February 1992 and concluded in 1995.

During the flight evaluation tests at Dryden, Langley provided technical support and on

two occasions provided rapid solutions to critical stability and control problems that had

stopped the flight tests.

Langley support of the X-31 included tests in the 30- by 60-Foot (Full-Scale) Tunnel,

the 20-Foot Vertical Spin Tunnel, the 12-Foot Low-Speed Tunnel, the 14- by 22-Foot

Tunnel, the 16-Foot Transonic Tunnel, the Jet Exit Test Facility, a radio-controlled drop

model, and piloted simulators.
Langley Contributions to the X-31

Rockwell-MBB X-31 215

LANGLEY CONTRIBUTIONS TO THE X-31

Background Langley participated in the X-31 Enhanced Fighter Maneuverability (EFM) Program

during four separate activities. From 1973 to 1984, Langley was active in the planning,

testing, and analysis of the remotely piloted Highly Maneuverable Aircraft Technology

(HiMAT) research vehicle. From 1984 to 1985, Langley cooperated in a program with

Rockwell International to develop a representative fighter configuration that could demonstrate the advantages of exploiting high-angle-of-attack maneuvers during close-in air

combat. From 1986 to 1991, Langley participated in the analysis and configuration

development of the International (United States and Federal Republic of (West)

Germany) X-31 Program. From 1991 to 1995, Langley supported the flight-test program, which was conducted at NASA Dryden Flight Research Center by the International Test Organization.

The HiMAT Program Following the Vietnam conflict and renewed emphasis on close-in air-to-air combat, the

U.S. military became interested in aircraft maneuverability. As a result, the requirement

for high speeds, long considered the key factor in successful air combat, became a secondary objective. NASA initiated a joint program with the Air Force known as the

Highly Maneuverable Aircraft Technology (HiMAT) Program. The staffs of the

Langley, Ames, and Dryden Research Centers all participated in planning the HiMAT

Program, with William P. Henderson serving as the technical lead and coordinator for

Langley. The focus of the HiMAT Program was flight research and maneuverability

demonstrations of a representative advanced configuration in the form of a remotely

piloted subscale vehicle at Dryden. The goals of HiMAT included a 100-percent

increase in aerodynamic efficiency over 1973 technology, and maneuverability that

would allow a sustained 8-g turn at a Mach number of 0.9 and an altitude of 25,000 ft.

The program ultimately achieved all goals.

The original HiMAT model with the thrust-vectoring,

wedge nozzle in the Langley 16-Foot Tunnel.
Langley Contributions to the X-31

216 Rockwell-MBB X-31

In August 1974, Rockwell International was awarded a contract to construct a reduced

scale model of the HiMAT design. Rockwell submitted a canard configuration with twin

vertical tails on a highly swept wing and a high aspect ratio, pitch thrust-vectoring,

wedge nozzle. The thrust-vectoring wedge nozzle was later replaced with a fixed, axisymmetric nozzle to reduce program costs. The first flight of the HiMAT occurred on

July 27, 1979, and research continued through January 1983. The success with the

HiMAT configuration inspired Rockwell to examine the benefits of a derivative fighter

that exploits high angles of attack for new tactical maneuvers during close-in air

combat.

The SNAKE Program In 1984, Rockwell proposed a cooperative program to Langley to assess and develop a

Rockwell advanced design known as the Super Normal Attitude Kinetic Enhancement

(SNAKE) configuration. Joseph R. Chambers and Joseph L. Johnson, Jr. determined

that the proposal was in concert with many Langley research interests in high-angle-ofattack technology, and the cooperative program on the SNAKE configuration was

begun. Langley researcher Mark A. Croom was assigned the role of lead engineer, and

he began a decade of personal participation in the X-31 evolution and flight-test

programs.

The initial SNAKE configuration bore a superficial resemblance to the earlier HiMAT

design (canard and wing-mounted twin vertical tails); however, the new configuration

was designed analytically with computers and a minimum amount of wind-tunnel tests.

Unfortunately, Croom’s aerodynamic tests of the initial SNAKE configuration in the

Langley 30- by 60-Foot (Full-Scale) Tunnel indicated unacceptable stability and control

characteristics. The configuration was unstable in pitch, roll, and yaw for all angles of

attack.

Based on their extensive experience with stability and control characteristics of

advanced fighters, Croom and Johnson provided the Rockwell team with several

recommendations to cure the problems exhibited by the SNAKE configuration. The

HiMAT during flight tests at Dryden.
Langley Contributions to the X-31

Rockwell-MBB X-31 217

The original Rockwell SNAKE configuration with

downturned wingtips and thrust vectoring paddles.

The modified SNAKE configuration after the Langley tests with upturned wingtips, wing

leading-edge flaps, enlarged vertical tails, enlarged wing-fuselage strake, and nose strakes.
Langley Contributions to the X-31

218 Rockwell-MBB X-31

configuration modifications resulted in satisfactory characteristics, and the aerodynamic

deficiencies of the initial SNAKE design had been eliminated. Rockwell was grateful

for the guidance and innovation contributed by Langley in the evolution of the SNAKE

configuration.

In the early 1980’s, an awareness of the benefits of thrust vectoring for dramatically

improved control at high angles of attack surfaced. In addition to studies of advanced

engine concepts with vectoring nozzles, interest arose over the use of simple thrustvectoring paddles in the engine exhaust to deflect the thrust for control augmentation.

As discussed in Langley Contributions to the F-14, the Navy, with Langley’s assistance,

had taken the lead in this area with flight tests on an F-14 modified with single-axis

yaw-vectoring paddles. In addition, during a cooperative program with Rockwell led by

Langley researcher Bobby L. Berrier, Langley provided design data for multiaxis thrustvectoring paddle configurations using the Jet Exit Test Facility in 1985. Based on these

fundamental research studies, Rockwell incorporated multiaxis thrust-vectoring paddles

into the SNAKE configuration. Free-flight tests of the modified SNAKE model in the

Full-Scale Tunnel by Croom’s team in 1985 provided an impressive display of the effectiveness of thrust vectoring at extreme angles of attack.

In West Germany, Dr. Wolfgang Herbst of Messerschmitt-Bolkow-Blohm (MBB)

aggressively touted the advantages of post-stall technology (PST) for increased

Modified SNAKE model flying at extreme angle of attack using

thrust vectoring in the Langley Full-Scale Tunnel.
Langley Contributions to the X-31

Rockwell-MBB X-31 219

effectiveness during close-in air combat. Herbst’s conclusions were based on windtunnel tests of a German advanced canard fighter configuration known as the TKF-90

and piloted simulator studies during which the application of simulated thrust vectoring

resulted in rapid directional turns at high angles of attack had increased the turn rate by

over 30 percent. Technical discussions between the Rockwell SNAKE Program managers and Herbst were initiated in 1983, and planning for a mutual program on PST

ensued. Discussions with the Defense Advanced Research Projects Agency (DARPA)

were very positive. When funding for collaborative international activities became available from the U.S. (the Nunn-Quayle research and development initiative in 1986) and

West German governments, the technical expertise of Rockwell and MBB were joined

under DARPA sponsorship in the X-31 Program. In view of Langley’s extensive experience in high-angle-of-attack technology, unique test facilities, and contributions to the

Rockwell SNAKE Program, DARPA requested in 1986 that Langley become a participant in the X-31 development program.

X-31 Configuration Evolution The Rockwell and MBB X-31 design team merged their configuration candidates into a

canard fighter powered by a single General Electric F404 engine with a single vertical

tail. The initial design included an F-16 canopy for cost-saving purposes. Extensive tests

of the initial X-31 configuration were carried out at Langley during 1987. These tests

included static wind-tunnel tests and configuration component evaluations in the

Langley 14- by 22-Foot High-Speed Tunnel, rotary-balance tests in the Langley 20-Foot

Vertical Spin Tunnel to determine aerodynamic characteristics during spins, and

dynamic force tests in the Langley Full-Scale Tunnel. Unfortunately, in 1988 the X-31

configuration was revised, and an F-18 canopy was incorporated. This change was

regarded as significant, and a major portion of the previous wind-tunnel tests had to be

repeated for the revised configuration.

Rotary-balance tests of the revised configuration were conducted in 1988, and spin tests

and static and dynamic tests were completed in 1989 for the updated configuration. In

1989, a 0.19-scale model of the X-31 underwent extensive aerodynamic and free-flight

tests in the Langley Full-Scale Tunnel. Results from these ground-based studies indicated that the X-31 might have marginal nose-down control at high angles of attack and

that the configuration might exhibit severe, unstable lateral oscillations (wing rock) that

would result in a violent, disorienting roll departure and an unrecoverable inverted stall

condition. Fortunately, the results also indicated that a simple control law concept could

prevent the aircraft from entering a spin. The awareness that such phenomena might

exist for the full-scale aircraft enabled the X-31 design team to configure the flight control system for maximum effectiveness.

An exhaustive test, which included 498 paddle and nozzle configurations of the multiaxis thrust-vectoring system, was conducted by Langley researcher Francis J. Capone in

the Jet Exit Test Facility during 1988. These data were used to select the final paddle

and nozzle multiaxis thrust-vectoring configuration. These data were also critical to the

design of the X-31 flight control system, since vectored thrust imposes large forces and

moments in addition to the normal aerodynamic parameters.

A 0.27-scale drop model was used by Langley to evaluate the post-stall and out-ofcontrol recovery characteristics of the configuration. The model, which weighed

about 540 lb and included extensive instrumentation, was flown without an engine

to assess the capabilities and characteristics of the basic airframe. The objective was

to demonstrate that the X-31 would be agile and have satisfactory characteristics without the additional augmentation provided by thrust vectoring. The drop-model test identifies characteristics and large amplitude flight motions that cannot be assessed in
Langley Contributions to the X-31

220 Rockwell-MBB X-31

X-31 with F-16 canopy during tests in the Langley 14- by 22-Foot Low-Speed Tunnel.

Free-flight tests of the X-31 in the Langley Full-Scale Tunnel.
Langley Contributions to the X-31

Rockwell-MBB X-31 221

conventional wind or spin tunnels. In the X-31 Program, the technique proved to be

invaluable as an early indicator of the highly unconventional behavior of the configuration. In particular, the violent roll departure indicated by tests of the free-flight model

was encountered during the drop-model tests. Several control schemes were evaluated

to eliminate this problem. In addition, the drop-model test technique provided solutions

to barrier problems during the full-scale flight-test program.

X-31 Flight Demonstration 

Program

The first flight of the first X-31 aircraft occurred at Palmdale, California, on October 11,

1990, and the second aircraft made its first flight on January 19, 1991. During the initial

phase of flight-test operations at the Rockwell facility at Palmdale, the two aircraft were

flown on 108 test missions. On the test missions, the aircraft achieved thrust vectoring in

flight and expanded the post-stall envelope to 40-deg angle of attack. Operations were

then moved to Dryden in February 1992, at the request of DARPA.

At Dryden, the International Test Organization (ITO) expanded the flight envelope of

the aircraft, including military utility evaluations that compared the X-31 to similarly

equipped aircraft for maneuverability in simulated combat. The ITO, managed by

DARPA, included NASA, the U.S. Navy, the U.S. Air Force, Rockwell Aerospace, the

Federal Republic of Germany, and Deutsche Aerospace (formerly MesserschmittBolkow-Blohm). The first NASA flight under the ITO took place in April 1992. As the

X-31 full-scale aircraft flight tests began at Dryden, the Langley staff maintained a close

support role for consultation and ground testing capability.

Two problems surfaced during the X-31 flight-test program, and both were considered

significant enough to curtail flight tests until solutions were found. The first problem

was encountered in the flight-test program when it became apparent that the pitch

control effectiveness of the aircraft at post-stall conditions (particularly at aft center of

gravity conditions) was marginal. Pilots reported that their ability to obtain positive,

crisp, nose-down aircraft response was unsatisfactory and that increased control effectiveness was required if the X-31 was to be considered tactically responsive at high

angles of attack. As part of the X-31 Team, Langley was requested to conduct windtunnel tests to explore options to provide the increased control at high angles of attack.

Mark Croom and his team quickly responded and evaluated 16 configuration modifications to improve nose-down recovery capability in the Full-Scale Tunnel. Results of the

One of the X-31 aircraft in flight.
Langley Contributions to the X-31

222 Rockwell-MBB X-31

Langley researcher Mark Croom (l) discusses the X-31

drop-model program with an X-31 program manager.

Mark Croom points to the aft-fuselage strakes defined by

Langley tests and subsequently incorporated on the X-31 aircraft.
Langley Contributions to the X-31

Rockwell-MBB X-31 223

investigation recommended that a pair of 6- by 65-in. strakes be mounted along the fuselage afterbody to promote nose-down recovery. The Langley recommendations, which

were given within a week of the test request, provided a timely solution to the problem.

The aft-fuselage strakes were incorporated in the X-31, and the pilots reported that the

nose-down control was significantly improved.

The second problem that occurred in the X-31 full-scale flight test was caused by large

out of trim asymmetric yawing moments at high angles of attack. Shortly into the highangle-of-attack, elevated-g phase of the envelope expansion, a departure from controlled

flight occurred as the pilot was performing a maneuver at 60-deg angle of attack. Data

analysis by the X-31 team indicated that a large asymmetric yawing moment, in excess

of the available control power, had triggered the departure. In response to an urgent

request for solutions, Croom and the Langley team conducted tests in the Langley FullScale Tunnel to design nose strakes that would minimize the problem. Once again,

Langley responded rapidly with a strake configuration that permitted the flights to

continue.

The X-31 Program logged an X-plane record of 524 flights in 52 months with 14 pilots

from NASA, the U.S. Navy, the U.S. Marine Corps, the U.S. Air Force, the German Air

Force, Rockwell International, and Deutsche Aerospace.

Evaluation of the X-31 as an enhanced fighter maneuverability demonstrator by the ITO

concluded in early 1995.

Role of the X-31 in HighAngle-of-Attack TechnologyThe accompanying photograph shows three thrust-vectoring aircraft, each capable of

flying at extreme angles of attack, cruising over the California desert in March 1994.

The F-18 HARV (top), the X-31 (middle), and the F-16 MATV (bottom) in flight.
Langley Contributions to the X-31

224 Rockwell-MBB X-31

The aircraft were flown in different programs and were developed independently. The

NASA F-18 HARV was a test bed for aerodynamic and buffet data at high angles of

attack to validate computer codes and wind-tunnel research. The X-31 was used to study

the ability of thrust vectoring and advanced displays to enhance close-in air combat

maneuvering. The F-16 Multiaxis Thrust Vectoring (MATV) aircraft was a demonstration of how thrust vectoring could be applied to an operational aircraft with an

advanced engine that has a vectoring nozzle.
The Future—Investing in Freedom 225

The Future—Investing in Freedom

As it looks to the future, the Langley Research Center intends to maintain a critical role

in support of industries and government agencies that are responsible for the development of technology for the defense of the United States. However, there are several challenges in striving to maintain this critical role.

The level of Langley support for military research and development is dynamic and flexible. Langley participates as requested in response to the unpredictable international and

domestic political and technical factors that influence our world as we enter a new millennium.

The reduction of U.S. military forces and plans for mergers or elimination of federal

research laboratories complicate planning for aeronautical research programs. The

numerous industrial mergers of the 1990’s have consolidated the number of aircraft

companies that request the results of NASA’s aeronautics efforts. Diminishing budgets

and personnel reductions have forced NASA to choose between space exploration and

aeronautics when placing priorities, which has resulted in fewer resources for traditional

military related research within NASA. Finally, maintaining world-class facilities in the

face of increasingly competitive foreign facilities is a great challenge.

The end of the Cold War has diminished the intensity of the arms race. However, the

alarming growth in international sales of sophisticated aircraft and arms to less developed countries and the development of advanced aircraft within nations such as the

former Soviet Union and China continue to pose a technological challenge to the air

supremacy of the United States.

The emergence of terrorist operations on a worldwide scale has changed the scope of

the potential threat to the United States. This change in scope demands a new look at the

adequacy of our military readiness and the requirements for new technology. For example, our experiences with uninhabited reconnaissance aircraft in Operation Desert Storm

and European peacekeeping missions were highly successful. This success highlights

the probability that uninhabited aircraft will increase in number in the future inventory

of the United States. Uninhabited aircraft permit unprecedented deviations from existing design constraints and radical improvements within technical disciplines such as

aerodynamics, structures, and flight controls.

Finally, the aging of the military aircraft fleet of the United States continues, and

replacement aircraft will eventually be required. Nearly all military aircraft that participated in Operation Desert Storm, Kosovo, and other peacekeeping missions of the
226 The Future—Investing in Freedom

1990’s were over 20 years old. Some research activities that contributed to the development of these aircraft began over 50 years prior.

Future military aircraft development programs for the United States will begin from the

extensive database of computer analyses, wind-tunnel tests, and flight-test results of past

and present military aircraft. Information is added to this database by fundamental

research conducted by Langley researchers. Very often this fundamental research points

the way to the solution of any problem that may occur in an aircraft development program. Shrinking budgets and staff reductions further encourage the use and expansion of

this database.

The staff at NASA Langley Research Center with their extensive aeronautical database

and experience is ready to provide the research that is needed to maintain the air superiority of the United States. With adequate funding, Langley will continue in partnership

with the Department of Defense, other government agencies, industry, and universities

to develop the next generation of high-performance military aircraft.
Wind Tunnels—The Tools of the Trade 227

Appendix

Wind Tunnels—The Tools of the 

Trade

NASA Langley Research Center’s world-class stature in aeronautics is a direct result of

the combination of the expertise and dedication of its staff and the unique test capabilities provided by its facilities. Throughout its long history, Langley has strived to anticipate requirements for new testing facilities, to conduct pilot testing of evolving facility

concepts, and to provide updated test capabilities during new aircraft development programs. As a result of these efforts, Langley offers high quality, unique test capabilities in

the areas of fundamental aerodynamics, aerodynamic performance, flight dynamics,

aeroelasticity and flutter, spinning, structures and materials, impact dynamics, aircraft

landing dynamics, and piloted simulators. 

The discussion of Langley contributions in the text of this document illustrates the critical roles and responsibilities that were assigned to the Langley facilities during the

development of these specific military aircraft. As might be expected, wind-tunnel facilities played a key role in the development process. Today, Langley operates wind tunnels that provide critical aerodynamic, flight dynamic, and aerothermodynamic data at

speeds ranging from low subsonic conditions to hypersonic conditions. Donald Baal’s

and William Corliss’ excellent review of NASA wind tunnels will provide the reader

with extensive information on these wind-tunnel facilities (ref. 5). 

The discussion of the military aircraft in this document reveals that certain Langley

wind tunnels provided most of the data for the development of these military aircraft.

These wind tunnels included the

• Langley 4- by 4-Foot Supersonic Pressure Tunnel

• Langley 7- by 10-Foot High-Speed Tunnel

• Langley 8-Foot Transonic Pressure Tunnel

• Langley 30-by 60-Foot (Full-Scale) Tunnel 

• Langley 16-Foot Transonic Tunnel

• Langley 20-Foot Vertical Spin Tunnel

• Langley 16-Foot Transonic Dynamics Tunnel

• Langley Unitary Plan Wind Tunnel

New wind-tunnel test capabilities, such as those provided by the National Transonic

Facility (NTF) at the Langley Research Center, and reductions in the NASA aeronautics

operating budgets in the 1990’s have resulted in the closure or transfer of the first four

Langley wind-tunnel facilities on this list. The remaining wind tunnels on the list are

still operating and providing valuable data for another generation of aircraft. Brief

descriptions of the listed wind-tunnel facilities follow.
Langley 4- by 4-Foot Supersonic Pressure Tunnel

228 Wind Tunnels—The Tools of the Trade

LANGLEY 4- BY 4-FOOT SUPERSONIC PRESSURE TUNNEL

Design work on the first large supersonic wind tunnel at Langley began in February

1945, with an effort to develop a 4- by 4-ft wind tunnel capable of providing test speeds

up to a Mach number of 2. Delayed by labor strikes and other difficulties, the tunnel did

not begin operations until May 1948. Initially powered by 6,000-hp motors (because of

limited electrical power at the time), the facility was repowered in 1950 with 45,000-hp

motors. Many historically significant military aircraft configurations and missiles were

tested in the facility, including the Century Series fighters (F-100, F-102, F-104, and

F-105), the TFX (precursor to the F-111), and the B-58 Hustler supersonic bomber.

The 4- by 4-Foot Supersonic Pressure Tunnel was dismantled in 1977, and its drive

motors, cooling towers, and support facilities were used in the construction of the

National Transonic Facility (NTF), which was built on the same site. NASA saved an

estimated $20 million in construction costs by utilizing the components of the old tunnel

to provide key elements for the new cryogenic NTF facility.

LANGLEY 7- BY 10-FOOT HIGH-SPEED TUNNEL

In 1945, Langley initiated operations in two 7- by 10-ft wind tunnels, which were built

side by side in the same building. One of these tunnels, known as the Langley 300-MPH

7- by 10-Foot Tunnel, was used for basic and applied aerodynamic research at speeds up

to 300 mph. The second tunnel, known as the Langley 7- by 10-Foot High-Speed Tunnel, was used for research at transonic test conditions.

The 7- by 10-Foot High-Speed Tunnel was the site of some of the most important

Langley aerodynamic research for military aircraft. Researchers utilized the facility to

conceive and develop breakthrough technical concepts such as the variable-sweep wing

and vortex-lift strakes. It was also used to assess and support the development of most of

the high-performance U.S. military fighters.

Regarded as one of the most productive research wind tunnels ever operated at Langley,

the 7- by 10-Foot High-Speed Tunnel was closed and dismantled in 1993 because of

limitations in operating budgets and workforce.

LANGLEY 8-FOOT TRANSONIC PRESSURE TUNNEL

Put into operation in 1953, the Langley 8-Foot Transonic Pressure Tunnel was used to

produce some of the most important aeronautical breakthroughs for civil and military

aircraft. Located on the original NACA property (East Area) at the Langley Air Force

Base, the facility was a follow-on to the 8-Foot High-Speed Tunnel and incorporated the

breakthrough slotted-wall concept for transonic testing. The new slotted tunnel was used

to develop supercritical wing technology, winglets, and other innovative concepts that

are now routinely used by military aircraft. Special test techniques, including the fluorescent oil flow visualization concept, were also developed and matured in the facility.

The tunnel was utilized extensively for the support of military aircraft programs, including the assessment of competing designs, analysis of the performance capabilities of

new configurations, and development of improvements and problem-solving concepts

for evolving aircraft.

Following a multiyear research investigation of hybrid laminar flow control, the 8-Foot

Transonic Pressure Tunnel was closed in 1995. The National Transonic Facility at the

Langley Research Center and the Langley 16-Foot Transonic Tunnel have now taken on

the transonic test workload.
Langley 30- by 60-Foot Tunnel

Wind Tunnels—The Tools of the Trade 229

LANGLEY 30- BY 60-FOOT TUNNEL

The design of the Langley 30- by 60-Foot (Full-Scale) Tunnel was initiated in 1929, and

the tunnel was put into operation in 1931 for the intended purpose of obtaining fullscale aerodynamic data for the biplane configurations of the day. The tunnel contributed

to military, commercial, and general aviation aircraft technology for over 64 years with

a wide variety of test techniques including free-flight tests of remotely controlled,

dynamically scaled models.

In 1985, the Langley Full-Scale Tunnel was named a National Historical Landmark.

NASA closed this historic wind tunnel in 1995 as a cost-saving action. It was subsequently transferred to the Old Dominion University, which now operates the facility for

a diverse customer base, including race car enthusiasts.

LANGLEY 16-FOOT TRANSONIC TUNNEL

Since becoming operational in 1941, the Langley 16-Foot Transonic Tunnel has undergone a series of improvements and upgrades. Initially capable of speeds up to a Mach

number of 0.7, the tunnel can now test over a speed range of up to a Mach number of

1.29. The 16-Foot Transonic Tunnel is an atmospheric, closed-circuit tunnel with an

octagonal test section that measures 15.5 ft across the flats. Twin 34-ft-diameter drive

fans provide power, and the tunnel has an exceptionally low disturbance level through

the transonic Mach number range. 

From its earliest operations, the facility has specialized in propulsion-airframe integration issues, ranging from propeller research and engine cooling research during World

War II to the design and integration of today’s advanced multiaxis thrust-vectoring and

reversing propulsion concepts. The breakthrough nonaxisymmetric (2-D) nozzle and

thrust-vectoring nozzle technologies were primarily developed in this facility. The availability of high-pressure airlines, water cooling lines, and hydraulic lines permit this

unique facility to conduct in-depth studies of powered advanced military configurations.

Because of the large test section, which results in low blockage values for typical models, this facility has also been extensively utilized for transonic aerodynamic studies on a

wide range of military aircraft. 

The 16-Foot Transonic Tunnel is operational and continues to contribute to military aircraft development programs. This tunnel operates in conjunction with an auxiliary test
Langley 20-Foot Vertical Spin Tunnel

230 Wind Tunnels—The Tools of the Trade

facility, known as the Jet Exit Test Facility, to provide design information for the development and maturation of innovative nozzle-propulsion system concepts and to support

specific NASA and Department of Defense aircraft development programs.

LANGLEY 20-FOOT VERTICAL SPIN TUNNEL

Following the initial operations of a 15-ft-diameter spin tunnel in 1935, Langley

designed and developed the Langley 20-Foot Vertical Spin Tunnel (Spin Tunnel)

and initiated operations in 1941. The Langley Spin Tunnel is a closed-throat, annular

return wind tunnel that operates at atmospheric conditions. The 12-sided test section is

20-ft across by 25-ft high. The test section velocity can be varied up to approximately

85 ft/sec. A 3-bladed, fixed-pitch fan powered by a 400-hp direct-current motor that is

located above the test section produces test section airflow. This motor is equipped with

a control system designed to allow rapid changes in fan speed, which results in rapid

flow accelerations in the test section. 

Dynamically scaled, free-flying models are used to investigate the spin and spinrecovery characteristics of aircraft configurations. To study spin characteristics, the

model is hand launched with prerotation into the vertically rising air stream. The tunnel

operator varies the tunnel speed so that the spinning model remains in equilibrium in

front of video cameras for documentation of results. Direct observation of the test article

is possible during tunnel operations via panoramic control room windows. The spinrecovery characteristics of aircraft are studied by using remote actuation of the model

aerodynamic control surfaces. The size of emergency spin-recovery parachutes systems

for flight test aircraft is also determined with specialized tests of scaled parachutes.

Free-spin data have been acquired in the Spin Tunnel and used by nearly all U.S. military fighter programs during and since World War II. The tunnel has now logged over

500 different aircraft studies. Nearly all U.S. attack and jet trainer programs have used

Langley free-spin test data.

In addition to free-spin tests, the facility permits the measurement of aerodynamic

forces and moments during spin conditions with a unique rotary-balance apparatus. In

addition to providing aerodynamic input data for analyses and theoretical studies of

spins, the rig has been used to provide electronically scanned pressures on models during simulated spin motions.
Langley 16-Foot Transonic Dynamics Tunnel

Wind Tunnels—The Tools of the Trade 231

The Langley 20-Foot Vertical Spin Tunnel is the only facility in the United States currently configured for free-spin tests and determination of emergency spin-recovery parachute requirements for military aircraft. The facility continues its service to the nation

for both military and civil spin studies. The majority of work, however, supports high

priority military aircraft programs.

LANGLEY 16-FOOT TRANSONIC DYNAMICS TUNNEL

The NASA Langley 16-Foot Transonic Dynamics Tunnel (TDT) became fully operational in 1960. It is now internationally regarded as the leading wind tunnel for performing flutter tests of large aeroelastically scaled full-span models at transonic speeds. The

TDT is the only facility in the world capable of studying a full range of aeroelastic phenomena at transonic speeds. The tunnel is used by the aircraft industry to clear new

designs for safety from flutter, to evaluate solutions to aeroelastic problems, and to

study aeroelastic phenomena at transonic speeds. The TDT is used to perform flutter

clearance investigations and to investigate flutter trends and aeroelastic characteristics

of fixed-wing and rotorcraft configurations. The TDT is also used to perform a variety

of active controls tests, to determine the effect of ground-wind loads on launch vehicles,

and to make steady and unsteady aerodynamic pressure measurements to support computational fluid dynamic (CFD) code development.

The TDT is a closed-circuit, continuous-flow wind tunnel capable of tests at stagnation

pressures from near zero to atmospheric and over a Mach number range up to 1.2. The

test section of the TDT is 16-ft square with cropped corners. One feature of the TDT

that is particularly useful for aeroelastic testing is a group of bypass valves that connect

the test section area to the opposite leg of the wind-tunnel circuit downstream of the

drive fan motor. In the event of model instability, such as flutter, these quick-actuating

valves are opened, which causes a rapid reduction in the test section Mach number and

dynamic pressure, which may result in stabilizing the model. Other features that make

the TDT uniquely suited for aeroelastic testing include high visibility of the model from

the control room, a highly sophisticated data acquisition system, flow oscillation vanes

upstream of the test section that can be used to generate sinusoidal gusts, a variety of

model mounting and suspension systems such as cantilever sidewall mounts for component models and a 2-cable-suspension system for full-span free-flying models, safety

screens that protect the tunnel fan blades from debris in case of a model failure, and

state-of-the-art instrumentation and test equipment.
Langley Unitary Plan Wind Tunnel

232 Wind Tunnels—The Tools of the Trade

Tests can be performed in the TDT with air as the test medium; however, the most distinguishing feature of the tunnel is the use of a heavy gas, presently R-134a refrigerant,

as the primary test medium. R-134a is about four times as dense as air, and yet sound

travels half the speed in R-134a as it does in air. These properties of higher density and

lower sonic speed have beneficial effects on the design, fabrication, and testing of

aeroelastically scaled wind-tunnel models that must accurately represent full-scale

counterparts. Physically larger models may be built, thereby simplifying the model fabrication process. The scaled natural frequencies of these larger models are lower, resulting in lower flutter frequencies, thereby reducing the risk of model destruction during

flutter. Other advantages resulting from the use of a heavy gas are a nearly three-fold

increase in Reynolds number and a lower tunnel-drive horsepower requirement.

The TDT has played a key role in the development process for virtually all military aircraft in the U.S. inventory, including transports and high-performance fighters. The

facility is extremely active and supports civil and military programs.

LANGLEY UNITARY PLAN WIND TUNNEL

The Langley Unitary Plan Wind Tunnel has been in continuous operation since construction was completed in 1955. Congressional approval for the tunnel was provided by

the Unitary Wind Tunnel Plan Act of 1949, which stated that the objective was to “Promote the national defense by authorizing a unitary plan for construction of transonic and

supersonic wind-tunnel facilities...” 

Developmental tests of virtually every supersonic military aircraft, missile, and spacecraft in the current U.S. inventory were performed in the Unitary Tunnel. In addition,

methods for predicting supersonic aerodynamic performance have been developed

through basic experimental fluid mechanics research conducted in the Unitary Tunnel.

The Unitary Tunnel is a closed-circuit pressure tunnel with two 4-ft by 4-ft by 7-ft test

sections, and a Mach number capability ranging from 1.47 to 4.63.

The Langley Unitary Plan Wind Tunnel participates in advanced military aircraft and

missile research. 
Bibliography 233

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7. Murri, Daniel G.; Nguyen, Luat T.; and Grafton, Sue B.: Wind-Tunnel Free-Flight Investigation of a Model of a Forward-Swept-Wing Fighter Configuration. NASA TP-2230, 1984.

8. Chipman, R.; Rauch, F.; Rimer, M.; Muniz, B.; and Ricketts, R. H.: Transonic Test of a Forward Swept Wing Configuration Exhibiting Body Freedom Flutter. AIAA-85-0689, 1985.

9. Fratello, David J.; Croom, Mark A.; Nguyen, Luat T.; and Domack, Christopher S.: Use of

the Updated NASA Langley Radio-Controlled Drop-Model Technique for High-Alpha Studies of the X-29A Configuration. A Collection of Technical Papers—AIAA Atmospheric Flight

Mechanics Conference, Aug. 1987, pp. 305–317. (Available as AIAA-87-2559.)

10. Raney, David L.; and Batterson, James G.: Lateral Stability Analysis for X-29A Drop Model

Using System Identification Methodology. NASA TM-4108, 1989.

11. Rivera, Jose A.; and Florance, James R.: Contributions of Transonic Dynamics Tunnel Testing to Airplane Flutter Clearance. AIAA-2000-1768, 2000.

Lockheed Martin C-130 Hercules

1. Petit, P. H.: An Applications Study of Advanced Composite Materials to the C-130 Center

Wing Box. Lockheed-Georgia Co., NASA CR-66979, 1970.

2. Yost, J. D.: Correction Factors for Miner’s Fatigue Damage Equation Derived From C-130

Fleet Aircraft Fatigue Cracks. AIAA-86-2684, 1986.

3. NASA and Industry-Partners in C-130 Technology. Researcher News, vol. 12, issue 23.

Langley Research Center, Nov. 27, 1998.

Lockheed Martin C-141 Starlifter

1. Ruhlin, Charles L.; Sandford, Maynard C.; and Yates, E. Carson, Jr.: Wind-Tunnel Flutter

Studies of the Sweptback T-Tail of a Large Multijet Cargo Airplane at Mach Numbers to 9.90.

NASA TN D-2179, 1964.

2. Sandford, Maynard C.; Ruhlin, Charles L.; and Yates, E. Carson, Jr.: Subsonic and Transonic

Flutter and Flow Investigations of the T-Tail of a Large Multijet Cargo Airplane. NASA TN

D-4316, 1968.

3. Sandford, Maynard C.; and Ruhlin, Charles L.: Wind-Tunnel Study of Deflected-Elevator

Flutter Encountered on a T-Tail Airplane. NASA TN D-5024, 1969.

4. Abel, Irving: Evaluation of a Technique for Determining Airplane Aileron Effectiveness and

Roll Rate by Using an Aeroelastically Scaled Model. NASA TN D-5538, 1969.

5. Cleveland, F. A.; and Gilson, R. D.: Development Highlights of the C-141 Starlifter.

AIAA-64-596, 1965.

6. Victor Crash. Aviat. Week & Space Technol., vol. 61, no. 4, July 26, 1954, p. 16.

7. Loving, Donald L.: Wind-Tunnel—Flight Correlation of Shock-Induced Separated Flow.

NASA TN D-3580, 1966.
240 Bibliography

8. MacWilkinson, D. G.; Blackerby, W. T.; and Paterson, J. H.: Correlation of Full-Scale Drag

Predictions With Flight Measurements on the C-141A Aircraft—Phase II, Wind Tunnel Test,

Analysis, and Prediction Techniques. Volume 1—Drag Predictions, Wind Tunnel Data Analysis and Correlation. NASA CR-2333, 1974.

9. Rivera, Jose A.; and Florance, James R.: Contributions of Transonic Dynamics Tunnel Testing to Airplane Flutter Clearance. AIAA-2000-1768, 2000.

Lockheed Martin C-5 Galaxy

1. Luoma, Arvo A.; Re, Richard J.; and Loving, Donald L.: Subsonic Longitudinal Aerodynamic Measurements on a Transport Model in Two Slotted Tunnels Differing in Size. NASA

TM X-1660, 1968.

2. Loving Donald L.; and Luoma, Arvo A.: Sting-Support Interference on Longitudinal Aerodynamic Characteristics of Cargo-Type Airplane Models at Mach 0.70 to 0.84. NASA

TN D-4021, 1967.

3. Patterson, James C., Jr.; and Flechner, Stuart G.: Jet-Wake Effect of a High-Bypass Engine on

Wing-Nacelle Interference Drag of a Subsonic Transport Airplane. NASA TN D-6067, 1970.

4. Parlett, Lysle P.; Fink, Marvin P.; and Freeman, Delma C., Jr. (appendix B by Marion O.

McKinney and Joseph L. Johnson, Jr.): Wind-Tunnel Investigation of Large Jet Transport

Model Equipped With an External-Flow Jet Flap. NASA TN D-4928, 1968.

5. Grantham, Willaim D.; Deal, Perry L.; and Sommer, Robert W.: Simulator Study of the

Instrument Landing Approach of a Heavy Subsonic Jet Transport With an External-Flow JetFlap System Used for Additional Lift. NASA TN D-5862, 1970.

6. Ruhlin, Charles L.; and Sandford, Maynard C.: Experimental Parametric Studies of Transonic T-Tail Flutter. NASA TN D-8066, 1975.

7. Thompson, William C.: Ditching Investigation of a 1/30-Scale Dynamic Model of a Heavy

Jet Transport Airplane. NASA TM X-2445, 1972.

8. Blackwell, James A., Jr.: Preliminary Study of Effects of Reynolds Number and BoundaryLayer Transition Location on Shock-Induced Separation. NASA TN D-5003, 1969.

9. McWhirter, H. D.; Hollenback, W. W.; and Grosser, W. F.: Correlation of C-5A Active Lift

Distribution Control System (ALDCS) Aeroelastic Model and Airplane Flight Test Results.

NASA CR-144903, 1976.

10. Rivera, Jose A.; and Florance, James R.: Contributions of Transonic Dynamics Tunnel Testing to Airplane Flutter Clearance. AIAA-2000-1768, 2000.

11. Perry, Boyd, III; Noll, Thomas E.; and Scott, Robert C.: Contributions of the Transonic

Dynamics Tunnel to the Testing of Active Control of Aeroelastic Response. AIAA-2000-

1769, 2000.

Lockheed Martin F-16 Fighting Falcon

1. Jackson, Charles M.: NASA/General Dynamics Cooperative Research Leading to and

Involving SCAMP. NASA Internal Report, May 1980.

2. Polhamus, E. C.: Application of Slender Wing Benefits to Military Aircraft. AIAA-83-2566,

1983.

3. Buckner, J. K.; Benepe, D. B.; and Hill, P. W.: Aerodynamic Design Evolution of the YF-16.

AIAA-74-935, Aug. 1974.

4. Nguyen, Luat T.; Ogburn, Marilyn E.; Gilbert, William P.; Kibler, Kemper S.; Brown, Phillip

W.; and Deal, Perry L.: Stimulator Study of Stall/Post-Stall Characteristics of a Fighter Airplane With Relaxed Longitudinal Static Stability. NASA TP-1538, 1979.

5. Peloubet, R. P., Jr.; and Haller, R. L.: Wind-Tunnel Demonstration of Active Flutter Suppression Using F-16 Model With Stores. AFWAL-TR 83-3046, Vol.1, 1983.

6. Foughner, J. T., Jr.; and Bensinger, C. T.: F-16 Flutter Model Studies With External Wing

Stores. NASA TM-74078, 1977.

7. Perry, Boyd, III; Noll, Thomas E.; and Scott, Robert C.: Contributions of the Transonic

Dynamics Tunnel to the Testing of Active Control of Aeroelastic Response. AIAA-2000-

1769, 2000.
Bibliography 241

Lockheed Martin F-22 Raptor

1. Mullin, Sherman N.: The Evolution of the F-22 Advanced Tactical Fighter. Wright Brothers

Lecture, AIAA-92-4188, 1992.

2. Aronstein, David C.; Hirchberg, Michael J.; and Piccirillo, Albert C.: Advanced Tactical

Fighter to F-22 Raptor—Origins of the 21st Century Air Dominance Fighter. AIAA, 1998.

Lockheed Martin P-3 Orion

1. Baals, Donald D.; and Corliss, William R.: Wind Tunnels of NASA. NASA SP-440, 1981.

2. Abbot, F. T., Jr; Kelly, H. Neale; and Hampton, Kenneth D.: Investigation of PropellerPower-Plant Auto-Precession Boundaries for a Dynamic-Aeroelastic Model of a FourEngine Turboprop Transport Airplane. NASA TN D-1806, June 1963.

3. Rivera, Jose A.; and Florance, James R.: Contributions of Transonic Dynamics Tunnel Testing to Airplane Flutter Clearance. AIAA-2000-1768, 2000.

Lockheed Martin S-3 Viking

1. Lee, Henry A.; and White, William L.: Spin-Tunnel Investigation of a 1/32-Scale Model of

the Lockheed S-3A Airplane—COORD No. N-AM-161. NASA TM SX-3057, U.S. Navy,

1974.

2. Rivera, Jose A.; and Florance, James R.: Contributions of Transonic Dynamics Tunnel Testing to Airplane Flutter Clearance. AIAA-2000-1768, 2000.

McDonnell Douglas F-4 Phantom II

1. Carmel, Melvin M.; and Gregory, Donald T.: Preliminary Investigation of the Static Longitudinal and Lateral Stability Characteristics of a Model of a 45 ̊ Swept Wing Airplane at Mach

Numbers of 1.59, 1.89, and 2.09. NASA MEMO 3-30-59L, 1959.

2. Carmel, Melvin M.; and Turner, Kenneth L.: Investigation of Drag and Static Longitudinal

and Lateral Stability and Control Characteristics of a Model of a 45 ̊ Swept Wing Airplane at

Mach Numbers of 1.57, 1.87, 2.16, and 2.53, Phase II Model. NASA MEMO 3-31-59L,

1959.

3. Oehman, Waldo I.; and Turner, Kenneth L.: Aerodynamic Characteristics of a 45 ̊ SweptWing Fighter-Airplane Model and Aerodynamic Loads on Adjacent Stores and Missiles at

Mach Numbers of 1.57, 1.87, 2.16, and 2.53. NACA RM L58C17, 1958.

4. Chambers, Joseph R.; and Anglin, Ernie L.: Analysis of Lateral-Directional Stability Characteristics of a Twin-Jet Fighter Airplane at High Angles of Attack. NASA TN D-5361, 1969.

5. Chambers, Joseph R.; Bowman, James S., Jr.; and Anglin, Ernie L.: Analysis of the Flat-Spin

Characteristics of a Twin-Jet Swept-Wing Fighter Airplane. NASA TN D-5409, 1969.

6. Ray, Edward J.; and Hollingsworth, Eddie G.: Subsonic Characteristics of a Twin-Jet SweptWing Fighter Model With Maneuvering Devices. NASA TN D-6921, 1973.

7. Moore, Frederick L.; Anglin, Ernie L.; Adams, Mary S.; Deal, Perry L.; and Person, Lee H.,

Jr.: Utilization of a Fixed-Base Simulator To Study the Stall and Spin Characteristics of

Fighter Airplanes. NASA TN D-6117, 1971.

8. Newsom, William A., Jr.; and Grafton, Sue B.: Free-Flight Investigation of Effects of Slats on

Lateral-Directional Stability of a 0.13-Scale Model of the F-4E Airplane—COORD No.

AF-AM-113. NASA TM SX-2337, U.S. Air Force, 1971.

9. Doggett, R. V.; and Hanson, P. H.: Wind Tunnel Buffet Pressure Investigation on the Lower

Nose Portion of the RF-4C Aircraft. NASA LWP-227, 1966.

Missiles

1. Blair, A. B., Jr.; Allen, Jerry M.; and Hernandez, Gloria: Effect of Tail-Fin Span on Stability

and Control Characteristics of a Canard-Controlled Missile at Supersonic Mach Numbers.

NASA TP-2157, 1983.

2. Blair, A. B., Jr.; and Rapp, G. H.: Experimental and Analytical Comparison of Aerodynamic

Characteristics of a Forward-Control Missile. AIAA-80-0374, 1980.
242 Bibliography

Rockwell B-1 Lancer

1. Newsom, William A., Jr.; and Grafton, Sue B.: Free-Flight Investigation of a 1/17-Scale

Model of the B-1 Airplane at High Angles of Attack—COORD No. AF-AM-128. NASA TM

SX-2744, U.S. Air Force, 1973.

2. Grantham, William D.; Deal, Perry L.; and Libbey, Charles E.: Piloted Simulator Study of the

Stability and Control Characteristics of the B-1 Airplane at High Angles of Attack—COORD

No. AF-AM-128. NASA TM SX-3381, U.S. Air Force, 1976.

3. Re, Richard J.; and Reubush, David E.: Effect of Several Airframe/Nozzle Modifications on

the Drag of a Variable-Sweep Bomber Configuration. NASA TM-80129, 1979.

4. Seiner, John M.; Manning, James C.; Capone, Francis J.; and Pendergraft, Odis C., Jr.: Study

of External Dynamic Flap Loads on a 6 Percent B-1B Model. ASME-PAPER-91-GT-236,

1991.

5. Rivera, Jose A.; and Florance, James R.: Contributions of Transonic Dynamics Tunnel Testing to Airplane Flutter Clearance. AIAA-2000-1768, 2000.

Rockwell X-31 Enhanced Fighter Maneuverability Demonstrator

1. Croom, M. A.; and Schnellenger, H. G.: High-Alpha Flight Dynamics of the X-31 Configuration. NASA CP-3149, 1990.

2. Knox, Fred D.: X-31 Flight Test Update. AIAA-92-1035, 1992.

3. Banks, Daniel W.; Gatlin, Gregory M.; and Paulson, John W., Jr.: Low-Speed Longitudinal

and Lateral-Directional Aerodynamic Characteristics of the X-31 Configuration. NASA

TM-4351, 1992.

4. Scott, William B.: X-31 Completes Post-Stall Test. Aviat. Week & Space Technol., vol. 138,

no. 20, May 17 1993, pp. 29–30.

5. Croom, Mark A.; Fratello, David J.; Whipple, Raymond D.; O’Rourke, Matthew J.; and

Trilling, Todd W.: Dynamic Model Testing of the X-31 Configuration for High-Angle-ofAttack Flight Dynamics Research. AIAA-93-3674, 1993.

6. Cobleigh, Brent R.: High-Angle-of-Attack Yawing Moment Asymmetry of the X-31 Aircraft

From Flight Test. NASA CR-186030, 1994.

Appendix

1. Perry, Boyd, III; Noll, Thomas E.; and Scott, Robert C.: Contributions of the Transonic

Dynamics Tunnel to the Testing of Active Control of Aeroelastic Response. AIAA-2000-

1769, 2000.

2. Cole, Stanley R.; and Garcia, Jerry L.: Past, Present, and Future Capabilities of the Transonic

Dynamics Tunnel from an Aeroelastic Perspective. AIAA-2000-1767, 2000.

3. Schuster, David M.; Edwards, John W.; and Bennett, Robert M.: An Overview of Unsteady

Pressure Measurements in the Transonic Dynamics Tunnel. AIAA-2000-1770, 2000.

4. Rivera, Jose A.; and Florance, James R.: Contributions of Transonic Dynamics Tunnel Testing to Airplane Flutter Clearance. AIAA-2000-1768, 2000.

5. Baals, D. D.; and Corliss, W. R.: Wind Tunnels of NASA. NASA SP-440, 1981.
Index 243

Index

A A-10 Thunderbolt II (Fairchild Republic) 57–60

A-12 Avenger (McDonnell Douglas and General Dynamics) 44, 87

A3 Skywarrior (Douglas) 24

A-6 Intruder (Grumman) 83–87, 90, 91, 93–95

A-7 (Ling Temco Voight) 38

A-9 (Northrop) 60

Abbott, Frank T. 141, 144, 170

Abel, Irving 76, 144

Abrupt Wing Stall (AWS) Program 49, 50

acoustic loads 137, 190

active lift distribution control system (ALDCS) 131

Actively Controlled Response of Buffet Affected Tails (ACROBAT) Program 43

Advanced Capability (ADVCAP) EA-6B aircraft 94

Advanced Composites Technology (ACT) Program 136, 137

Advanced Fighter (VFX) Program 98, 100

Advanced Manned Strategic Aircraft (AMSA) Program 205, 207

Advanced Medium Range Air-to-Air Missile (AMRAAM) 195, 196, 199

Advanced Medium STOL Transport (AMST) Program 24

Advanced Tactical Fighter (ATF) Program 159–163, 207

Advanced Tactical Transport (ATT) Program 24

Advanced Trainer (VTX) Program 53

aeroelastic divergence 109–112, 119

aileron buzz 172, 174

aileron reversal 139, 140, 143, 144

air bag 76, 77

Air Combat Fighter (ACF) 35

Air Force Flight Dynamics Laboratory 79, 81, 192

Air Mobility Command 28, 140

Aircraft Energy Efficiency (ACEE) Program 27

Aircraft Landing Dynamics Facility, see Langley Aircraft Landing Dynamics Facility

Alford, Jr., William J. 36, 65, 100, 188

Alford, William L. 154

Allen, Jerry M. 197

Allison, Dennis O. 93

Ames Research Center 12, 20, 28, 35, 38, 60, 67, 79, 91, 93, 137, 138, 188, 215

Ames Research Center 12-Foot Pressure Tunnel 60, 73, 115

antisubmarine warfare (ASW) 167–169, 171–173

area rule 71, 101, 187

Armstrong, Neil A. 17

artificial stabilization 13

Attack Experimental (A-X) Program 57–60
244 Index

Attinello, Dr. John 16

augmented deflector exhaust nozzle (ADEN) 43, 44, 120–122

Australia 29, 43, 167, 175, 245

automatic rudder interconnect (ARI) 104, 105

AV-8 Harrier (Boeing) 11–13, 16–18, 20, 42

Aviation Week and Space Technology 67, 141

Ayers, Theodore G. 67–69, 78, 79, 81, 210

B B-1 Lancer (Rockwell) 61, 151, 205–212

B-2 Spirit (Northrop Grumman) 201–203

BAC 111 27

BAI Aerosystems, Inc. 5–9

Bare, E. Ann 56

Batterson, James G. 118

Bauer, Steven X. S. 49

Bedford, William 14

Bell Aircraft Corporation 63

Bennett, Robert M. 170

Berrier, Bobby L. 72, 107, 121, 189, 192, 193, 210, 218

Blackwell, Jr., James A. 133, 138, 145, 160, 163

Blair, Jr., Adolphus B. 197

Bland, Samuel R. 170

blow-in door 70

Bobbitt, Percy J. 92, 93

Boeing 11, 12, 21, 23, 25, 29, 30, 32, 47, 50–53, 56, 66, 81, 86, 87, 125, 126, 160, 161, 

163, 176, 186, 206, 214

Boisseau, Peter C. 72

Boswinkle, Robert W. 170

Bowman, Jr., James S. 73, 74, 91, 102, 181, 183, 191, 210

Bristol Siddeley 13

British Aerospace 11, 43, 52–54

Budiansky, Bernard 119

buffet 30, 32, 39, 40, 42, 43, 45, 78, 79, 80, 106, 149, 151, 165, 166, 175, 178, 183, 

192, 224

C C-130 Hercules (Lockheed Martin) 22–24, 135–138

C-141 Starlifter (Lockheed Martin) 23, 124, 125, 129, 133, 139, 140–145

C-17 Globemaster III (Boeing) 21–28, 124, 129

C-5 Galaxy (Lockheed) 22, 23, 123–133, 143, 145

cable-mount 48, 106, 144

camber, variable 32

Camm, Sir Sydney 15

Campbell, James F. 150

Campbell, John P. 13, 23, 24, 63, 138

Canada 29, 43, 245

canard 19, 102–104, 121, 149, 150, 193, 197, 216, 219

Capone, Francis J. 72, 193, 212, 219

Carden, Huey D. 77

Cargo Experimental (CX) Program 23

Carmel, Melvin M. 177

Cazier, Jr., Frank W. 155

Chambers, Joseph R. 53, 73, 112, 180, 182, 216, 245

Champine, Robert A. 17

Cheney, Richard 87

cockpit display 117, 136, 137
Index 245

Cole, Stanley R. 87

Collier Trophy 22, 30, 148, 202, 206

composite material 21, 27, 28, 119, 191

computational fluid dynamics 30, 40, 49

Concorde 149

Conner, D. William 170

control augmentation system (CAS) 191

convergent-divergent (CD) nozzle 43, 44

Corlett, William 197

Cornelius Aircraft Company 111

Cornell Aeronautical Laboratory 8-Foot Transonic Pressure Tunnel 69

Corson, Jr., Blake W. 189

cranked-wing 188

Creedon, Dr. Jeremiah F. 138

crew escape module 62, 76, 77

Croom, Mark A. 117, 216, 218, 221–223

Culpepper, Richard G. 16, 18

D D6ac steel 78

Daugherty, Robert H. 55

David Taylor Research Center (Navy) 40

Davis, Randall C. 137

DC-10 27

Deal, Perry L. 16, 210

deep stall 21, 27, 28, 147, 152–154

Defense Advanced Research Projects Agency (DARPA) 108–110, 112, 119, 120–122, 

192, 213, 214, 219, 221

Defense Department Research and Engineering 187

Department of Defense (DOD) 1, 2, 23, 24, 32, 38, 41, 43–46, 49, 57–59, 61, 62, 67, 

81, 90, 97–99, 107, 120, 121, 125, 147, 149, 159, 161, 175, 183, 185–189, 192, 

195–197, 206, 212, 226, 230

Deutsche Aerospace 221, 223

Dexter, H. Benson 137

Diederich, Franklin W. 119

digital cockpit 52

digital flight control system (DFCS) 39, 105

dihedral 141, 176–178, 182

ditching tests 131, 132

dog tooth 177

Doggett, Jr., Robert V. 119, 183

Donely, Philip 170

Donlan, Charles J. 63, 65, 69

Dragon Drone 6, 8, 9

drooped horizontal tail 16, 182

drop model 30, 36, 37, 47, 48, 62, 74, 75, 103, 110, 112, 117, 118, 157, 176, 181, 182, 

191, 206, 209, 214, 219

Dryden Flight Research Center 28, 32, 38–42, 62, 67, 79, 80, 81, 98, 105, 110, 115, 

116, 120, 138, 149, 155, 188, 190, 191, 213–216, 221

Dutch roll 7

E EA-6 Prowler (Grumman) 85, 89–95

Edwards Air Force Base 33, 35, 59, 60, 74, 153, 157, 182, 193

EF-111 62

effects of test section size 69, 125

Elber, Wolf 78
246 Index

electronic warfare 62, 89, 91, 171, 172

elevator 7, 27, 70, 139, 140, 142, 143

empennage 23, 27, 30, 75, 86, 95, 130, 138, 141, 142, 150

engine inlet 51, 52, 56, 70, 99, 103, 109, 110, 119, 187, 202, 203

engine-fuselage fairing (pancake) 101

Enhanced Fighter Maneuverability (EFM) Program 108, 214, 215

Erickson, Gary E. 40, 45, 46, 49

Exdrone BQM-147A (BAI) 5–9

externally blown flap (EBF) 21, 23–25, 124, 128, 129, 138

F F/A-18 High Alpha Research Vehicle (HARV) 39, 40–42, 122, 223, 224

F/A-18 Hornet (Boeing) 29–32, 35–46, 87, 106

F/A-18E/F Super Hornet 29, 30, 41, 42, 44–50

F-105 (Republic) 66, 67, 178, 228

F-111 Aardvark (General Dynamics) 30, 44, 61–63, 66–81, 100, 188, 192, 228

F-14 Tomcat (Grumman) 35, 38, 40, 61, 68, 70, 97–108, 188, 218

F-15 Eagle (McDonnell Douglas) 38, 39, 44, 61, 104, 122, 148, 151, 158, 160, 161, 

185–194, 207, 212

F-15 Short Takeoff and Landing and Maneuver Technology Demonstrator (STOL/

MTD), see Short Takeoff and Landing and Maneuver Technology 

Demonstrator (STOL/MTD)

F-16 Fighting Falcon (Lockheed Martin) 31, 38, 39, 112–114, 147–153, 155, 156, 179, 

219, 220, 223

F-16 Multiaxis Thrust Vectoring (MATV) aircraft 223, 224

F-16E 157

F-16XL 147, 148, 156–158

F-22 Raptor (Lockheed Martin) 61, 106, 135, 137, 159–161, 163–166, 190

F-4 Phantom II (McDonnell Douglas) 35, 38, 175–184, 190, 191, 199, 245

F-5 (Northrop) 31, 32, 102, 114, 115

F-8 Crusader (LTV) 78, 155

F9F Panther (Grumman) 154

Fairchild Republic 57, 58

fairing 27, 31, 49, 50, 69, 70, 101, 141, 142, 183, 184, 210, 211

falling leaf 36

Farmer, Moses G. 48, 106, 155, 174, 191, 192, 211

fatigue 61, 78, 84, 87, 93, 131, 136, 137, 190

Fatigue and Fracture Laboratory 62, 78

Federal Republic of (West) Germany 12, 16, 43, 214, 215

Ferris, James C. 81, 92

fin 92, 123, 130, 142, 176, 180, 182, 195, 199

flap hinge 27

flaperon 114

flat spin 60, 61, 74, 97, 102–104, 118, 153, 175, 181–183

Flechner, Stuart G. 127

Fletcher, Dr. James 75

flight control computer 37, 39

flight control system 13, 24, 27, 28, 32, 33, 39, 47, 73, 74, 97, 104, 105, 109, 114, 115, 

117, 152–154, 203, 205, 210, 214, 219

Flight Dynamics Laboratory, see Air Force Flight Dynamics Laboratory 

flight envelope 13, 17, 26, 32, 35, 48, 49, 87, 107, 142, 143, 152, 155, 163, 221

flow field 40, 70, 86, 151, 180, 208

flutter 21, 26, 29, 30, 42, 43, 48, 61, 62, 70, 75, 76, 79, 80, 83, 84, 86, 87, 97, 98, 100, 

106, 120, 124, 129, 130, 139, 140–144, 147, 155, 157, 167–172, 174, 185, 186, 

191, 192, 195, 197, 199, 205, 206, 211, 227, 231, 232
Index 247

fly by wire 154

forward-swept wing (FSW) 39, 109–115, 119, 120

Foster, Dr. John 100, 187, 188, 189

Foster, John V. 42

Foughner, Jerome T. 155

Fowler flap 128

Fratello, David 7

free-flight model tests 11, 14, 18, 33, 36, 37, 63, 72, 112, 129, 208, 214

Frink, Neal T. 138

Full-Scale Tunnel, see Langley 30- by 60-Foot (Full-Scale) Tunnel

G Garrick, I. Edward 170

General Aviation Stall-Spin Program 8

General Dynamics 35, 58, 59, 61, 62, 66, 68–73, 78, 79, 81, 87, 100, 112, 148, 155, 

160, 161, 163, 210

General Electric 29, 57, 97, 109, 120, 123, 147, 171, 175, 201, 205, 208, 213

General Electric F404 engine 219

General Electric YJ101 engine 121

Gilbert, William P. 33, 38, 74, 75, 152, 191

Gilman, Jean 174

Glenn Research Center (Lewis) 28, 38, 44, 67, 121, 138, 188, 193

Global Positioning System (GPS) 8

Gloss, Blair B. 149

Grafton, Sue B. 32, 33, 112, 113, 115, 156, 162, 164, 180, 208

Grantham, William D. 210

graphite-epoxy 27

ground effect 13, 25, 59

Grumman 58, 59, 64, 66, 68–71, 81, 83–85, 89–91, 94, 97, 98, 100, 101, 103, 104, 106, 

109, 110, 112, 115, 116, 119, 120–122, 173

H Hahne, David E. 92, 93

Hall, Robert M. 46, 49, 50

Hallissy, James B. 79, 81

Hanson, Perry 183

Hardrath, Herbert F. 78

Harris, Jr., Roy V. 49, 156, 188

Hassell, James L. 65

Hawk aircraft 54

Hawk missile 195

Hawker Aircraft Ltd. 13

head-up display 28

Henderson, William P. 31, 59, 121, 149, 150, 193, 210, 215

Herbst, Dr. Wolfgang 218, 219

High-Angle-of-Attack Technology Program (HATP) 29, 30, 38–41, 108

Highly Maneuverable Aircraft Technology (HiMAT) 112, 215, 216

horizontal tail 16, 27, 36, 48, 69, 75, 83–85, 100, 103, 104, 129, 139, 142, 143, 150, 

152, 153, 177, 182, 183, 185, 187, 191, 208

Horne, Walter C. 144, 184

Hudson, Charles M. 78

hybrid wing 31, 150

hydraulic control system 21

hydroplaning 139, 140, 144, 175
248 Index

I Impact Dynamics Research Facility, see Langley Impact Dynamics Research Facility

inlet 13, 51, 52, 56, 69–71, 99, 103, 109, 110, 119, 187, 202, 203

Institute of Defense Analyses 16

interfairing 70, 71, 99, 187–189

International Test Organization (ITO) 215, 221, 223

J Jackson, Charles M. 156, 197

Johns Hopkins University Applied Physics Laboratory (JHU-APL) 6, 7

Johnson, Jr., Joseph L. 7, 23, 25, 92, 93, 122, 128, 138, 157, 193, 216

Jones, Lisa E. 77

Jordan, Jr., Frank L. 92, 93

Ju-287 (Junkers) 111

K Kayten, Gerald G. 24

Kestrel (XV-6A) 12, 16–18

Krone, Jr., Dr. Norris J. 112, 119

Kuhn, Richard E. 13, 20

Kvaternik, Raymond G. 155

L Lamar, John E. 31, 150

landing gear 35, 52, 53, 133, 183

Langley 12-Foot Low-Speed Tunnel 7, 30, 52–54, 62, 72, 90, 92, 112, 180, 214

Langley 14- by 22-Foot Subsonic Tunnel 30, 109, 110, 119

Langley 16-Foot Transonic Dynamics Tunnel (TDT) 22, 26, 30, 42, 43, 48, 62, 75, 76, 

79, 80, 83, 84, 87, 97, 98, 106, 109, 110, 119, 120, 123, 124, 129–131, 

139–144, 148, 149, 155, 157, 165–172, 174, 176, 183–186, 188, 191, 192, 199, 

202, 206, 211, 227, 231, 232

Langley 16-Foot Transonic Tunnel 12, 13, 30, 40, 43, 44, 50–52, 56, 62, 64, 65, 69–72, 

79, 83–85, 90, 93, 98, 100, 101, 107, 124, 127, 130, 161, 186, 188–190, 193, 

196, 202, 206, 210–212, 214, 227–229

Langley 20-Foot Vertical Spin Tunnel (Spin Tunnel) 18, 30, 32, 33, 36, 47, 52, 54, 55, 

58, 60, 62, 64, 73, 83–85, 89–91, 98, 102, 110, 112, 115–117, 148, 149, 151, 

153, 157, 160–165, 171–173, 176, 181, 182, 186, 188, 191, 199, 202, 203, 206, 

210, 214, 219, 227, 230, 231, 245

Langley 26-Inch Transonic Blowdown Tunnel (Blowdown Tunnel) 62, 75

Langley 30- by 60-Foot (Full-Scale) Tunnel 12–14, 18, 22–24, 30, 32, 36–38, 46, 62, 

65, 70, 72, 73, 90–93, 98, 110, 112, 114, 121–124, 128, 129, 148, 149, 

151–153, 157, 160–165, 176, 180, 182, 186, 188, 191, 193, 202, 206, 208, 209, 

214, 216, 218–221, 223, 229, 245

Langley 300-MPH 7- by 10-Foot Tunnel 22, 23, 63, 64, 111, 228

Langley 4- by 4-Foot Supersonic Pressure Tunnel 62, 64, 98, 161, 186, 188, 189, 196, 

197, 227, 228

Langley 6- by 28-Inch Transonic Tunnel 90, 92

Langley 7- by 10-Foot High-Speed Tunnel 27, 30–32, 57–59, 62, 64, 65, 89, 90, 93, 94, 

98, 100, 148, 149, 157, 176, 178–180, 186, 188, 199, 227, 228

Langley 8-Foot Transonic Pressure Tunnel 22, 25, 30, 34–36, 45, 62, 64, 68–70, 79, 81, 

98, 100, 125, 127, 133, 138, 145, 196, 206, 210, 227, 228

Langley Acoustic and Dynamic Laboratory 190

Langley Aircraft Landing Dynamics Facility 144, 184

Langley Control Line Facility 13

Langley Differential Maneuvering Simulator (DMS) 30, 33, 40, 42, 47, 98, 104, 107, 

110, 112, 115, 117, 148, 149, 151–153, 157, 245

Langley Impact Dynamics Research Facility 18, 19, 62, 76, 77
Index 249

Langley Jet Exit Test Facility 30, 40, 122, 214, 218, 219, 230

Langley Low-Turbulence Pressure Tunnel (LTPT) 90, 92

Langley Plum Tree Test Site 8

Langley Unitary Plan Wind Tunnel (Unitary) 62, 68, 70, 79, 98, 100, 148, 149, 157, 

160–163, 165, 175–177, 186, 188, 196–199, 227, 232

Langley V/STOL Tunnel 18, 20

leading edge 5–8, 11, 31, 36, 37, 43, 45, 49, 51–54, 92, 104, 150, 151, 157, 163, 

177–180, 191, 217

leading-edge extension (LEX) 29, 31, 32, 34–37, 39, 40, 45, 46

leading-edge slats 54, 92, 175, 176, 178, 179, 181

Leavitt, Laurence D. 193

Lee, Henry A. 85, 91, 173

LFAX-10 188

LFAX-4 99, 100, 188

LFAX-8 185, 187, 188

LFAX-9 188

Lewis Research Center, see Glenn Research Center

Libbey, Charles E. 74, 75, 103, 181, 182, 191, 208

Lightweight Fighter (LWF) 32, 33, 35, 148, 149, 151

liquid crystal flat-panel display 135–137

Lockheed 23, 123–126, 128, 131, 135–141, 143, 145, 160–163, 165, 167–173

Lockheed L.188 Electra 167–170

Lockheed Martin 124, 135–140, 147–149, 159, 172

Lockwood, Vernon E. 59

Loftin, Jr., Laurence K. 67, 100

Long Range Combat Aircraft (LRCA) 212

Loving, Donald L. 125, 133, 144

Luckring, James M. 31, 150

Luoma, Arvo A. 125, 133

M main landing gear 27, 133

maneuvering flaps 31

Margason, Richard J. 18

Mason, Mary L. 193

mass balancing 143, 155, 191

McClellan Committee 67

McDonnell Douglas 12, 20–23, 25–30, 32, 35–37, 40, 42, 45–49, 52–54, 87, 100, 160, 

175, 176, 178, 182, 183, 185, 186, 188–193, 199

McGhee, Robert J. 92

McKinney, Linwood W. 59, 149, 150

McKinney, Marion O. 13, 14, 103

McKinney. Linwood W. 31

McMillin, S. Naomi 50

McNamara, Robert S. 66, 68

Mercer, Charles E. 72, 79, 85, 93

Messerschmitt-Bolkow-Blohm (MBB) 43, 213, 214, 218, 219, 221

Miller, David S. 156, 197

missiles 3, 18, 59, 76, 84, 161, 172, 177–179, 195–197, 199, 228

Mission Adaptive Wing (MAW) Program 61, 62, 81

Moore, Frederick L. 181

Morello, Samuel A. 16

Moses, Robert W. 43, 165

Moul, Martin T. 27

multiaxis vectoring 193

Murri, Daniel G. 46, 115

Mutual Weapons Development Program (MWDP) 12, 13, 16
250 Index

N NA-39 66

NACA 6-series airfoil 78

nacelle 23, 27, 59, 123, 125, 127, 212

NASA Headquarters 17, 20, 24, 121, 122, 138, 207

National Advisory Committee for Aeronautics (NACA) 64, 67, 119, 228

National Aeronautics and Space Act 1

National Transonic Facility (NTF) at Langley 26, 90, 93, 110, 202, 203, 227, 228

Naval Air Systems Command 18, 42, 100

Naval Weapons Center, China Lake, California 197

Newman, Jr., James C. 78

Newsom, Jr., William A. 151, 208

Nguyen, Luat T. 33, 38, 104, 107, 114, 115, 152, 153

Nichols, Mark R. 67, 100, 207

Nicks, Oran W. 25

noise 136, 137

nonaxisymmetric nozzle 44, 121, 159, 192

North American Rockwell 18, 100, 188, 208

North Atlantic Treaty Organization (NATO) 12, 13, 15, 65

Northrop Grumman 29, 30, 84, 90, 110, 188, 201–203

nose vibrations 183

nozzle 12, 13, 16, 17, 20, 40, 43, 44, 69–71, 85, 107, 120–122, 159, 161, 187, 189, 190, 

192, 193, 205, 206, 211, 212, 216, 218, 219, 224, 229, 230

nozzle, two-dimensional, see two-dimensional (2-D) nozzle

O Ogburn, Marilyn E. 157

Operation Desert Storm 6, 8, 90, 148, 179, 225

oscillation 104, 118, 143, 163, 174, 181, 205, 211, 219, 231

P P.1127 (Hawker Siddely) 11–16

P.1154 15, 16

P-1101 (Messerschmitt) 63

P-2 Neptune 168, 169

P-3 Orion (Lockheed) 167–170

Patriot missile 195, 196

Patterson, Jr., James C. 127

Patuxent River Naval Air Station 36, 37, 39, 44, 48, 53, 55, 105, 107, 108, 182

Paulson, Jr., John W. 119

Pendergraft, Jr., Odis C. 72, 193, 212

Persian Gulf 172

Person, Jr., Lee H. 16, 17

Petersen, Richard H. 160, 163

pilot-induced oscillation (PIO) 51, 55

pitch rocker technique 153

pod 23, 27, 70, 91, 92, 101

Polhamus, Edward C. 31, 32, 36, 63, 65, 67, 69, 70, 149, 150, 180

porosity 49, 50

powered-lift 16, 18, 22, 25, 28, 138

Pratt and Whitney 21, 61, 71, 83, 89, 139, 147, 159, 185, 193

Project Agile Eagle 179

R radar 37, 90, 106, 179, 188, 199, 206

Raney, David L. 118

Ray, Edward J. 31, 149, 150, 178, 180, 181
Index 251

Re, Richard J. 72, 125, 193, 211

recognition visit 28, 138

Reed, Jr., Wilmer H. 119, 144, 155, 170

Reeder, John P. (Jack) 12, 13, 15–17

relaxed static stability 110, 114, 152

Remotely Piloted Vehicle (RPV) 3, 5, 6, 8, 9

Reubush, David E. 107, 211

Reynolds number 60, 73, 115, 125, 133, 191, 232

Ricketts, Rodney H. 119, 120

Rivera, Jr. Jose A. 87

Robins, A. Warner 188

rollerons 195, 197

rotary-balance 47, 163, 219, 230

Royal Aircraft Establishment 17

rudder 7, 24, 27, 41, 43, 83–86, 91, 104, 107, 129, 142, 152, 165, 191

Ruhlin, Charles L. 26, 76, 79, 129–131, 141, 143, 157, 174, 211

Runckel, Jack F. 67, 70, 71

runway grooving 140, 144, 175, 184

S S-3 Viking (Lockheed) 171–174

Sandford, Maynard C. 76, 79, 129–131, 141, 143

sawtooth notch 8

Sawyer, Wallace C. 197

Schade, Robert O. 14

Scher, Stanley H. 60

Seamens, Robert 189

Seiner, John M. 190, 212

semispan model 26, 87, 127, 128

Sewall, William G. 92, 94

Sewell, Charles 104

Shaw, David S. 68

Short Takeoff and Landing (STOL) 11, 22, 23, 25, 27, 28, 138

Short Takeoff and Landing and Maneuver Technology Demonstrator (F-15 STOL/

MTD) 122, 185, 190, 192–194

sidestick controller 147, 154, 155

Sidewinder missile 195, 197, 198

single expansion ramp nozzles (SERN) 43, 44

skid, landing 7

slat 14, 54, 93, 104, 178–180

snag 36, 45, 54, 177

spar 111, 123, 130, 142

Sparrow missile 195, 199

Spearman, M. Leroy 67, 69, 197

speed brake 46, 83–85, 92, 93

speed bump 71, 101

spin 8, 12, 18, 20, 30, 32, 33, 36, 38, 39, 41, 42, 47, 51, 52, 54, 55, 57, 58, 60–62, 

73–75, 83–86, 89, 91, 93, 97, 98, 102–105, 112, 115, 116, 118, 119, 147, 153, 

154, 157, 159, 160, 162–164, 171–173, 175, 178, 180–183, 185, 186, 190, 191, 

195–197, 199, 203, 208, 210, 213, 214, 219, 230, 231, 245

spin recovery parachute 33, 39, 47, 102, 116, 153, 162, 165, 181

stabilizer, horizontal 27, 85

stabilizer, vertical 27

Stack, John 13, 15, 64–67

stall 7, 8, 36, 39, 49, 53, 54, 56, 57, 74, 91, 93, 111, 112, 119, 136, 138, 173, 175, 180, 

183, 210, 219, 245
252 Index

stall inhibitor system (SIS) 61, 73, 74

Stallings, Jr., Robert L. 197

stealth 6, 87, 160, 161, 202

sting interference effects 125

stores 47, 48, 58, 60, 75, 76, 80, 84, 87, 90, 155, 177, 195, 196, 199

strakes 32, 37, 41, 60, 106, 115, 150, 217, 222, 223, 228

Structures Division 27

Subsonic Low Altitude Bomber (SLAB) Program 207

Super Normal Attitude Kinetic Enhancement (SNAKE) configuration 216–219

supercritical wing technology 21, 26, 61, 62, 78, 80, 228

Supersonic Cruise and Maneuver Prototype (SCAMP) 156, 157

Supersonic Cruise Integrated Fighter (SCIF) Program 156

Swallow configuration 64, 65

T T-45 Goshawk (Boeing) 51–56

Tactical Fighter Experimental (TFX) Program 62, 66, 67, 228

tail flutter 61, 123, 129, 130, 140–143, 191

Taylor, Robert T. 27

tethered hover test 18

Thompson, William C. 133

thrust vectoring 16, 30, 38, 40, 41, 44, 85, 107, 108, 193, 214, 217–219, 221, 224

thrust-vectoring vanes 40

tires 52, 55

titanium 87

Toll, Thomas A. 65

Tosti, Louis P. 14

trailing edge 20, 29, 32, 36, 54, 56, 65, 81, 86, 90, 92, 93, 128, 129, 137, 138, 143, 145, 

147, 149, 151, 178

transition 13–15, 145

transition point 145

Transonic Aircraft Technology (TACT) Program 61, 62, 78–81

trim drag 68, 100

T-tail 21, 23, 27, 28, 124, 125, 129, 130, 139–143

tumbling 109, 116, 117

turbofan 21, 23, 97, 125, 201

turbojet 23, 84

turboprop 135, 167–169

two-dimensional (2-D) nozzle 44, 190, 192, 193, 229

U U.S. Air Force 9, 21–24, 26, 28, 31–33, 35, 42, 44, 57–62, 64–66, 69–71, 73, 74, 

76–81, 109, 110, 112, 119, 120, 123, 125, 128, 133, 135, 137–141, 144, 

147–149, 152, 153, 155, 156, 158–162, 165, 175, 176, 178, 180, 182, 183, 185, 

186, 188–190, 192, 193, 198, 199, 201, 202, 205–208, 210–212, 215, 221, 223, 

228, 245

U.S. Army 8, 124, 129

U.S. Marine Corps 5–9, 11–13, 18, 29, 83, 86, 89, 135, 175, 176, 178, 223

U.S. Navy 8, 18, 20, 24, 29, 31, 35–37, 39, 40, 42–44, 46–56, 62, 65, 66, 69, 70, 83, 

85–87, 89–91, 94, 97, 98, 100, 102–105, 107, 120, 121, 135, 141, 147, 

167–169, 171–173, 175–180, 182, 183, 190, 192, 198, 199, 213, 218, 221, 223, 

245

Uninhabited Air Vehicle Joint Project Office (UAV-JPO) 8

United Kingdom 9, 11–13, 15–18, 21, 43, 64, 245

upper-surface blowing (USB) 25, 138

upper-surface shock waves 26
Index 253

V vapor screen system 40

variable-sweep wing 61–63, 65–68, 97, 99, 106, 111, 187, 207, 211, 228

Vectoring in Forward Flight (VIFF) 11, 12, 16–18

Vehicle Enhancement Program (VEP) 94

ventral fin 185, 189

Vertical and Short Takeoff and Landing (V/STOL) 11–16, 18, 20, 43, 107, 120, 245

vertical tail 5–7, 24, 32, 40, 43–45, 48, 86, 90–92, 101, 106, 129, 141, 142, 151, 163, 

165, 166, 175, 177, 178, 185, 189, 193, 216, 217, 219

Vietnam 32, 38, 59, 84, 149, 176, 178, 179, 183, 215

vortex 31, 142, 149, 150, 157

vortex flow 31, 39–41, 72, 150

vortex lift 29, 31, 147, 149, 150, 157, 228

W Waggoner, Edward G. 93

Wallops Flight Facility 8, 48, 144, 196, 197, 199

wedge nozzle 215, 216

Whipple, Raymond D. 55, 115, 116

Whitcomb, Dr. Richard T. 20, 25, 26, 35, 36, 69, 71, 78, 79, 101, 125, 133, 138, 144

White, Ronald 190

White, W. Louis 73, 173

Wilmoth, Richard G. 72

wind tunnel to flight correlation 18, 144, 190

wing box 78, 81, 131, 135–137

wing drop 7, 29, 30, 48–51, 53, 54

wing pivot 64, 65, 68, 78

wing rock 104, 105, 109, 113–115, 118, 219

wing stall 27, 180, 208

winglet 21, 25–28, 228

wingtip 7, 8, 16, 25, 85, 92, 111–113, 155, 192, 195, 197, 199, 217

Wood, Richard M. 197

Wusk, Mary Beth 138

X X-1 (Bell) 17, 63, 111

X-29 (Grumman) 39, 109–122

X-31 (Rockwell-MBB) 108, 122, 213–216, 219–224

X-5 (Bell) 63, 64

XF-10F (Grumman) 64

XFG-1 (Cornelius Aircraft Company) 111

XFV-12A (North American Rockwell) 11, 18–20

Y YA-10A 58

YA-9A 58

Yager, Thomas J. 144, 184

Yates, Jr., E. Carson 141, 142

YC-14 23, 25

YC-15 23–26

Yetter, Jeffrey A. 49

YF-16 32, 33, 35, 147–153, 155, 156

YF-17 29–37, 42–44, 149, 192

YF-22 159–163

YF-23 160, 161

Yip, Long P. 7, 8, 53, 54

Monographs in Aerospace History 255

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256 About the Author

About the Author

Joseph R. Chambers is an aviation consultant who lives in Yorktown, Virginia. He

retired from the NASA Langley Research Center in 1998 after a 36-year career as a

researcher and manager of military and civil aeronautics research activities. He began

his career as a specialist in flight dynamics as a member of the staff of the Langley 30-

by 60-Foot (Full-Scale) Tunnel, where he conducted research on a variety of aerospace

vehicles including V/STOL configurations, reentry vehicles, and fighter aircraft configurations. He later became a division chief with responsibilities for all research projects

in the Full-Scale Tunnel, the 20-Foot Vertical Spin Tunnel, drop-model tests, and piloted

simulator studies in the Differential Maneuvering Simulator (DMS) at Langley. When

he retired from NASA, he was manager of a division that conducted systems analysis of

the potential payoffs of advanced aircraft concepts and research investments.

Mr. Chambers participated in the development of virtually every Air Force and Navy

aircraft of the past 30 years, including all fighter-attack aircraft. He is the author of over

50 technical reports and publications and coauthor of NASA Special Publication SP-514

on the subject of airflow condensation patterns for high-performance aircraft. He has

made presentations on research and aircraft development programs to audiences as

diverse as the Von Karman Institute in Belgium and the annual Experimental Aircraft

Association (EAA) Fly-In at Oshkosh, WI. He has served as a representative of the

United States on international committees for military research and has given presentations in Japan, China, Australia, the United Kingdom, Canada, Italy, France, Germany,

and Sweden.

Mr. Chambers received the Exceptional Service Medal and the Outstanding Leadership

Medal, two of NASA’s highest awards. He received the Arthur Flemming Award in 1975

as one of the 10 Most Outstanding Civil Servants for his management of NASA stallspin research for military and civil aircraft. He also was a corecipient of the 1973

H.J.E. Reid Award presented by Langley for the most outstanding technical paper (an

analysis of the lateral-directional stability of the F-4 fighter aircraft at high angles of

attack). In 1977, he was a corecipient of the Mechanics and Control of Flight Award of

the American Institute of Aeronautics and Astronautics. This award was presented for

his contributions to technology to predict high-angle-of-attack, stall, and spin characteristics for aircraft and for improving those characteristics through combined aerodynamic and automatic control design. Mr. Chambers has a bachelor of science degree in

Aeronautical Engineering from the Georgia Institute of Technology and a master of science degree in Aerospace Engineering from Virginia Polytechnic Institute and State

University (Virginia Tech).